Q: thinking of buying a truck with 300K miles,well maintained etc. would it be a good idea?

The thing to look at is this is a full size truck with a small V6 engine size. This engine would have worked harder than a larger V8 engine would have. This does not mean the engine is bad but something to think about. If you look at how good the truck was taken care of is the main thing. Do they have maintenance logs or receipts to show any major repairs and maintenance was done. The mileage is only a concern if the truck was not taken care of. Look for oil leaks on any part of the drive train. You could get a mechanic to do a pre-purchase inspection. This may help you with your decision and may point out a major problem with the truck.