Truck is new to me and I've had the 92 for years. So, I look under the dash and notice the classic trailer brake controller wiring, good! And I'm thinking "this truck has to have had a tuner" but I don't know what to look for under the dash or in the engine bay. Would be nice just to have to get a display

 

Most tuners on the 3rd gens are software so you wouldn't see anything. There are a few module types, most would have a piggy back connector towards the rear of the valve cover if I recall correctly.

 

If it wasn't software upload look for signs of wires being pull through through the firewall, Velcro on the fuse box under the hood, broken clips on the injector harness, signs the column has been separated.