I just spent 2 months looking for a tahoe. A few things I noticed are this.
#1
People put new tires on trucks to hide screwed up front ends. Usually, People dont put money into things they are trying to get rid of so if someone puts new tires on a truck theyre selling Its a RED FLAG!
#2
If the truck is from anywhere north of NJ it will be covered in rust. look under the hood, If it has it, youll see it.
#3
There is a seal where the front wheel drive shaft comes out of the 4 wheel drive gear box. (I do not know technical names) That seal was leaking on alot of used trucks I looked at. Im told its relatively cheap to fix. (Depending on how long its been leaking and if there is any fluid left inside)
#4
I would have someone who knows body work look at it to see if its been painted. A clean Carfax doesnt mean anything. IF someone had an accident and paid out of pocket to have it fixed, carfax wouldnt know about it.
#5
There are a bizillion trucks on the market with gas prices rising, if it isnt exactly what your looking for, dont buy it! What your looking for is out there!
Hope this helps... Just things I realized or came across while looking....
If I think of anything else Ill add it....