popular upgrades in the mid 90's
 

So I was finally able to buy this 89 cummins 5 spd dually. The truck have been towing a 40ft gooseneck trailer since 93. The previous owner said when he bought it in 93 it wouldn't tow that trailer with any power. He said he took it in to a shop (not sure what kind) and they "did something" to the injection pump, injectors, and Turbo. I haven't tore into the engine yet but out of curiosity I pulled the intake tube off the turbo and saw 8 blade and the nut on the shaft doesn't look like the holes nuts. The turbo housing is still stamped h1c. After brief research I leared that turbo should have 7 blades. Sorry for the story but my question is, what were the popular upgrades done in the early to mid 90s that might have been performed on this engine?

Does the exhaust housing have a wastegate? (stock H1C does not)

Does it have a 3" or 4" compressor inlet? (stock 89 is 3")

Fuel pin, governor spring, timing advance, and bigger injectors are common mods. Fuel pin is easy to inspect, so are the timing marks (compare marks on timing case to inj pump)

It does not have a wastegate and it's a 3" inlet. The turbo still has the h1c tag on it which leads me to believe that only the internals were touched. what would they have done to the turbo in say '94?

'94 is a WH1C - basically the big H1C (91.5-93) with a 12cm wastegated housing.

There always seems to be a newer/better model year Holset turbo to put on, so most people swap to a newer version rather than messing with the internals.