The door hinges on the gmt400 are crap. Hinges are welded on too. As for the rest nothing that can't be remedy easily. Starters and alternator were not great.
I never liked that series of trucks much.
The door hinges were terrible, the outside door handles were barely any better. And they were a pain to replace!
The front axle actuator (heater) was junk, then they came out with the solenoid which improved it some.
The recirculation door actuator was terrible to deal with.
A one 3500 truck get the frame folded on a lift once. A service bed on the back.
I loved the NV4500 and the CS130 alternators, and the permanent magnet gear reduction starters showed up during the GMT400. The CS130 needs and Iceberg case to be as reliable as the earlier SI units, but they kick butt in output power for the day.
The GMT800 is so much better!!
Incredibly easy to work on the doors, window regulators and outside handles. The doors will come off in sort order to do bushings when needed.
Headlights come out in seconds to swap bulbs, steering columns are fairly easy to work on.
My son and I swapped the main underdash wiring harness in his '01 for a fully optioned one in an afternoon. The cleaning did slow us down some, and then swapping the parts in the doors took another half of a day. There are things to be mindful of, yes. But overall it went well.
There are some expensive things that can fail, though.
