The GT5S was effectively a cosmetically updated GT5 with smoothed out fenders and wraparound front spoiler, S apparently denoting the new cars steel-formed bodywork. Under the skin the GT5S incorporated all those upgrades applied to the GT5, most importantly the larger ventilated front disc brakes and reinforced suspension. The Pantera’s two-seat sheet steel monocoque chassis hadn’t changed much since 1971 but nevertheless ticked all the right boxes. There was independent double wishbone suspension with coil springs, telescopic dampers and anti-roll bars all round. Campagnolo’s gorgeous 15-inch light alloy wheels were again shod with Pirelli P7’s. At 13-inches across, the rear P7's were a match for the Countach whilst the ten-inch fronts were even wider making the unassisted steering pretty physical at low speeds. Stuffed into the engine bay was Ford’s familiar 351 cubic inch V8. Although nothing fancy compared to thoroughbred European units, the single overhead camshaft pushrod operated Cleveland got the job done admirably and offered massive scope for tuning. At the time of the GT5S introduction, De Tomaso were still using up their supply of American-built Cleveland’s leftover from when Ford pulled out in 1974. Displacement was 5763cc thanks to a bore and stroke of 101.6 x 89mm respectively, two states of tune having been available: a 300bhp entry-level motor with the standard Ford Motorcraft carb or the more commonly used full fat 350bhp unit.

Still undeniably macho, the bulbous wheelarches and redesigned front spoiler were now smoothly integrated instead of looking like a body kit glued on to an original narrow-body Pantera. As usual, the bodyshells were fabricated at considerable expense by Carrozzeria Embo of Modena, nice details including the slatted brake cooling ducts carved out from each rear wheelarch and auxiliary Carello driving lights housed in the deep front spoiler. Standing barely 43-inches high, the GT5S was visually a match for the most decadent Latin exotics of the eighties but also had a certain beauty that evaded the GT5. Inside the two cars were identical, both blending finely crafted fixtures and fittings with rudimentary parts-bin switchgear arranged in the same haphazard manner as those very first Pantera’s. Leather covered the plush seats, transmission tunnel, dash top, door trims and centre console, air conditioning and electric windows being fitted as standard along with central locking and electric mirrors. The chunky three-spoke leather-rimmed Momo steering wheel slightly obscured the tops of the speedo and tach, these being set into a wooden dash that further enhanced the cabins luxurious feel. Despite such a well-appointed interior, the GT5S was no boulevard cruiser and in 350bhp trim could hit 158mph flat out. 0-60mph took a mere 5.3 seconds with 0-100 coming up in 12.6.

Right-hand drive examples started rolling out of the factory in 1985, chassis 9388 having been the earliest. Meanwhile, after the split with Ford in 1974, De Tomaso hadn't officially exported any cars to the US. A handful of grey market vehicles had since made their way across the Atlantic but the prohibitively expensive cost of meeting North American emissions legislation was cited as the main reason for De Tomaso officially withdrawing from what should have been the firms biggest market. Recognising this, Kirk Evans of Ohio established Amerisport and between 1985 and ’87, gave US customers the opportunity of buying a brand new and fully licensed GT5S. Thanks to his close ties with the De Tomaso factory, Evans was able to make a deal that saw fully assembled cars minus engines sold direct to Amerisport where rebuilt emissions-legal Cleveland V8’s were installed. Because these cars were exported to the US incomplete, they were classed as sub-assembly parts and avoided the need for costly Federal approval. On arrival at the Amerisport works, each car was fitted with a rebuilt Cleveland V8 featuring a host of emissions equipment. This included a special air box that enclosed the Holley carburettor, custom headers and catalytic converters. They were then EPA and DOT certified and sold as new, the first Amerisport GT5S having been chassis 9381 which was unveiled in April 1985 at the annual POCA meet in Las Vegas.

De Tomaso had enough leftover from the Ford deal to last several years, but when these ran out, the firm were forced to source Cleveland engines from Ford Australia who continued to build a limited number for various applications. Featuring a tougher block with thicker main webbing, they were the motors of choice for many NASCAR teams but otherwise remained largely identical to the US-made Cleveland’s. By 1987, the supply of Aussie blocks had dried up too and De Tomaso were forced to find another alternative for the last three years of GT5S production. Ford’s Windsor 351 seemed to be the most appropriate unit and with a compression ratio of  8.5:1, made 300bhp at 6000rpm. Like the Cleveland, Windsor V8’s could be specified with a variety of hop-up parts including solid or hydraulic lifters, large or small-port heads, special exhaust manifolds and a wide choice of cams and carburetion. Production continued until 1990 when the last GT5S (chassis 9562) was despatched to its lucky first owner. By this time, 89 cars had been completed at the factory in Modena (21 of which are believed to have been right-hand drive). A further 25 to 40 partially finished cars were sold to Amerisport taking overall GT5S production to around 120 units.