Versatile Farmer:

Sounds like your 1993 is a PEEC electronic engine. If so, then there is newer software/chip to improve "RPM overshoot" during start-up.

CAT calls their chip a "Personality Module"; back then.

Another possibility, is that the rack BTM(brushless torque motor) is erratic, or the mechanical rack bar is sticky, or your have the older style BTM that its little arm (that fit inside the collar on the servo linkage) is binding, thus the BTM can't control rpms correctly.[Just had one of these issues 6 months ago=old technical bulletin about this]

Another advantage, of the latest software/chip, is that there is some protection built into the software, that in the event that the timing advance fails and goes to "maximum timing advance"; then the software will derate the engine ,so you don't melt down the aluminum pistons!!!

If it is an ALL mechanical engine,Serial number prefix of "3ZJ";  then I would look at sticky rack bar, or scored servo in the governor. All mechanical engines should not overshoot in rpm much if even at all. That's why I assume you have a PEEC engine(s/n prefix="4CK").