Front end vibrations
Any unusual sounds except the chirp if you shut if off
Check oil
Check blow-by
shift the transmission manually through each gear making sure it engages
make sure all exterior lights are functional
check under the truck for major leaks like a rear main seal leak
If he has any paper work on it, go through it

Most important, he made you the offer. So if you want to take a day and thank about it after you check it out, he won't be pressured to sell it off fast because he want's your truck. So take your time, no matter what kind of sales pitch he serves you.

 

Great Advise .... definatly a real good idea to weigh out the options .. pro's and con's and such