Anouther thing with a slight pull to the right is that most road surfaces are crowned so that the water will run off of it during a rain.
Find a nice straight stretch of road, and with no traffic (DUH!) Run your truck right down the centerline of the road. It should track fairly true there...a little more on the left and it should start drifting left, a little to the right and it should start drifting right. This is with a "neutral" alignment. I'm pretty sure that some cars are spec'd to bias the alignment a little to the right too...for whatever reasoning. Or maybe that's just how some shops do them?
My 97 has a fairly neutral alignment...it won't drift if I center line the truck on a good road, but in the right lane it will slowly track to the shoulder.
If it's a mild to severe pull and things are aligned properly, I'd also check out the caliper on that right front. It's possible that the caliper mount got knocked around enough so that it will bind and not release fully when you're off the brakes. Have seen this on GM RWD cars before...if the slider bolts get rusty or tweaked, the caliper won't operate as it should and cause rotor drag.
I doubt having a flat up front would throw off the rear axle alignment...it usually takes some pretty serious banging around to knock a leaf-sprung solid axle out of position.