My truck has 3.73's with 285's it's marginal at best, I'm sure some will talk shyt but it would be better with 4.10's Put it more in the powerband.
If the top end been done with a cam etc yeah tuning would be in order, but that's not going to fix lugging along in o/d. On/off gas constantly.
Fleet trucks amd vans mostly. I have driven a few of them, with the 4.10 gear they are not as gutless as one would assume. The base engine even in the P30 box vans was the 4.3L. The old UPS P30 dually box trucks had a 4.3L with a Q-Jet and a 4spd manual for years. They were carbureted until about 90-92.
When I lived in DE. went to state/muni auction. Fleet/municipal tracks are bare bones , no frills, stripped down trucks, no power anything. It's been a few years but some of those rusted out trucks were 3/4 ton and did some duty as salt spreaders. some had plow set -ups 40-50k mileage on them but holes in the bed you could fit your head through. bed sides flapping in the breeze. Figured I could score something to yank a drive train out But 4.3 and lighter duty 4l60 that go behind them was not what I was looking for. There just wasn't anything there.
To this day fleets can order just about any combination or lack of amenities they so choose. The dealer I got my 2019 from was known as a fleet supplier. The 19 had the smaller info screen, heat and a/c and that was about it. 4.3/8 speed/3.73. Just basic no frills, I have to move shyt around truck.
Guys that buy 80-100k decked out trucks to work, beat, abuse, and wholesale/trade off..... 3-5 years later for 30-40k maybe, have lost their minds.
You could still get a 2500 4x4 reg cab 4.3 a year or 2 ago, dealers won't order them. In 19-20 it was a 35k truck and 80k crew cab ones pay better. Offer 5 or 10k off an 80k truck and people will line up thinking there getting something for nothing.