i have a 1990 chevrolet 2500 2wd. it has the 3.73 rear gear and a four speed trans.
Do you mean a 4 speed manual trans or automatic?
If automatic, you’re already where you want to be.
If converting to automatic, then there might be some issues with the ECM. Not that this year of 700R4 was electronically shifted but the ECM’s prom and wiring harness may not accommodate for the torque converter’s lock up clutch(TCC).
Not all that big of a deal, you could always just add a manual lock up switch and turn it on when you’re at highway speeds.
If a 700R4 or any lock up trans isn’t allowed to go into lock up, the trans will run overheated and likely burn up the fluid.
Dan.
Canadian "EH"