Tim's right - Pilot bearing/bushing. And Greemmachine - start it with trans in gear, clutch pedal depressed, brakes applied. The bushing may be stuck, and just need broken free and "excercised".
I recently replaced the engine/trans powerpack in wife's Jeep,and had the same thing - for the first few miles - now all is fine.
You MAY have to pull trans and re-lube the bushing, but I bet you'll be OK without.
Warlock - shouldn't you be buying engine parts or sumpin? (yeah, there could be contaminants "sticking" the clutch top the flywheel or PP, but I'm giving the dude the benefit of the doubt and assume he cleaned it all up before assembly. UNLESS he used some NOS parts and cosmolene dripped out of hidden crevisses and is acting like glue - you may be on to something, there.
"other peoples junk, is something or other" - Militarypotts 02/07/2011