My friends dad bought a 1993 Dodge Cummins 3/4 ton. It way out powered everything else on the road. But an ancient truck that rode like a tank. He didn't like Ford or want another 3/4 ton. So he bought a 93 GM 1/2 ton 4x4, the only thing a 6.2 was acceptable for, a huge turd compared to the Cummins. My BIL Dodge 93 1 ton Cummins dually added bigger pump, injectors and a 3" stack, really moved after that. I drove a 85 GM 6.2 4spd 1/2 2wd work truck with Granny low, so basically a 3 spd. It was Ok even in -40 and acceptable performance. The 6.9 and 7.3 was mostly decent even in -40.Before 89 when Dodge put the cummins in the D250, the IDI 6.9/7.3 was the BEST powerplant for a 3/4 or 1 ton pickup. It was that or a gas hog 460, weak 454 or turd 6.2 in a GM, or an anemic 360 in a dodge.
GM didn't have a diesel worth owning until they put in an Isuzu (cough duramax cough)
Dodge cabs felt like you were stepping back into 1972 until 1994 when they went to the new cab.
Not sure what kind of life the ambulance has had, but i wouldn't be concerned.