wise advice
The best bet that you can do check the truck over really well... differentials transfer case oil trans fluid... 140,000. On these 350s really isn't all that bad. They will last forever if they are well maintained or even semi well maintained. It all depends on how the truck was taken care of by its previous parent lol. I have a 94 burban that I just bought with 149,000 and after going over it very thoroughly I ended up making an amazing purchase. As long as there are no leaks from the differentials and the transfer case then the 4wd should be sound. Checking the oil and the coolant should give you a good idea of how the motor was taken care of. You don't want to see perfectly clean oil because that could be someone hiding a problem but at the same time you don't want the oil to look like s*** because then it could be an indicator of poor maintenance. Coolant should be nice and green not brown... and make sure that the transmission fluid is bright red like strawberry syrup...