Hello everybody. I want to know if I should buy this truck or not.
It is a '92 GMC Sierra 1500(I think 1500). The seller wants $4,000.

When I first looked at it, the odometer read 77k. The tires looked ok. I saw what looked like tranmission fluid(reddish) dripping from the chasis.
The back bumper and tailgate(which reads "Chevrolet") has been replaced.

When I met the private seller, to take the truck for a test drive, he told me he's only done basic maintenance on the truck and that the air conditioner needs to be recharged(is not working). He told me that the back bumper had to be replaced because of a ding in it(or something like that) and the tailgate was replaced because the old one's paint is wearing off.

He opened the hood and told me he bought the truck at an auction and did not know its history except that the original V6 engine has been replaced with a V8. He told me he wasn't sure if the 77k on the odometer is the orginal miles, because he thinks the miles might have been changed when the engine was. (I don't think this is likely. Does anyone else reading this think it is?)

He said the truck has been good so far and that he didn't use it except to haul a small trailer around.

I wanted to take the truck on the interstate for the test drive and he told me he didn't have time, so I didn't make a big deal about it. He had to start the truck with a battery booster. He told me the battery was new, but the truck had not been started in a while and this was normal. I wonder about this.

I got the truck to go around 50mph, and it seemed fine. The truck drove smoothly. Of course, the windows were rolled down, so I couldn't hear all of the engine during the drive(I didn't think of this at the time. I probably should have made him roll up the windows and sweat the drive out.)

The truck seemed to shake a bit when it idled and the brakes seemed a little stiff and hard to push to get the truck to brake. He told me he just had new brakes put on it. I don't have a lot of experience with trucks, but I would think newer brakes would be pretty easy to push.

I haven't took the truck to a mechanic to have it inspected yet, and I have the VIN but haven't done a CARFAX report on it yet(I'm not sure if it's worth the trouble at this point).

What do you think? Anything sound wrong to you here? Any advice?