One more question....does the 3.9's idle rough. I test drove two and counting the one I bought and I think that they idle rough. They both ran down the road alright and was smooth, but seem to idle rough.

Is this nature of them or?

The one my parents had idled smooth. Maybe not as buttery smooth as some but definitely not rough.

Most of them do tend to idle rough, one cylinder being a touch off has a bigger effect on the whole when it is one out of 6 than 1 out of 8. Also the chains stretch and the plastic gear wears a lot and that retards the valve timing causing low vaccume and rough idle. A nice tight chain should also help the MPG by closeing the intake valve earlier(actually where it is intended to close) and helping to build cyl preasure, it will also let the MAP sensor know there is not as much load on the engine as it thinks there is based on a weak vaccume signal, if vaccume is weak it thinks there is more load and dumps more fuel.

It's never gonna idle as smooth as a 60 degree v-6, but they seem to be rpm sensitive as far as smoothness goes. Those chains usually can be heard rattling at idle when they're getting too loose.

I've owned a '95 3.9, A-500, 3.23 reg cab and a '01 3.9, 5 speed, 3.55 ext cab and they were both consistent 20 mpg trucks (50/50 city/hwy driving), as opposed to my '97 5.2, A-500, 3.92 reg cab at 14-15 mpg. I towed my Spirit on an open trailer the 80+ miles to Norwalk several times with the '01 with no problems - it wasn't a Cummins, but it had decent power. Odd thing about the '01 - it got poor mileage and had no power till it hit 500 miles, then it was like you flipped a switch; I got noticeably better mileage and power, as if it had a "valet mode" in the computer so you couldn't abuse it until it hit a certain mileage and was broken in.

I think that I'm getting around 14 if I'm lucky with it right now. I've also noticed that goes into overdrive at 30 is this normal?