195k on my 99 4.0.
replaced the tranny at 185k (the reverse band snapped. i regularly would let the truck roll backward while throwing it into drive. it works on these trannys because the reverse band serves as sort of a clutch, but its not good for it. best to stop fully before putting it in drive again. otherwise the tranny would have still been working perfect).
ive also replaced the normal things like balljoints, exhaust and one wheel bearing. otherwise, surprisingly, basically no work on the motor at all- just spark plugs, wires and serpentine belts a couple times..... and about 3 batteries (i run a lot of electronics that tend to malfunction and drain the battery flat a lot).
the damn thing still runs like its new (and because i keep up on the balljoints, it also rides like new) im really shocked how well it still runs, and that everything still works (electric door lock actuators are too weak to be useable anymore, but those only cost $30 a side). i always thought this truck would really start falling apart around 200k, but honestly it seems like its just broken in. the motor shows ZERO signs of upcoming trouble, no oil leaks anywhere, no consuming oil even if i go 5k miles between changes.
i guess the only real part that doesnt work right is the tachometer. that might just be a bad connection though, as it works on and off constantly while im driving, sometimes only shows 1krpm or so when its really 2krpm... band your hand on the dash and it pops back up to normal for a bit.
i think a big reason its stayed as good as it has is because of regular up-keep. replace your balljoints and stuff when they first go bad, because having those loose and shaking around causes other things on the truck to go bad prematurely.
as far as the motor, replace the sensors when they go bad and use good oil. also fuel system cleaners every oil change helps a lot too. and also, suck out your power steering resivior and refill with fresh fluid every oil change! (new trick i learned from here. its more important then it seems).