We just got a gem at the dealership!

A 1999 F-250 Superduty with the 5.4 liter gas engine. Automatic trans. Rear wheel drive.....and it's got twin I-beams! I never knew the superduty trucks were built with twin beams. It was taken for inspection today....and will hit the lot within a few days. We're asking 4k for it. Only has 112k miles.
Should I buy it? I don't really want a car payment...so I'm hoping someone talks me out of it....but on the other hand. It's a pretty huge upgrade on my current two wheel drive. Hmmm....