Does the trigger bar lean against the right side of the frame (looking towards the muzzle)? It should.
What V1 parts did you get? They shouldn't make any difference, unless these parts came from a P30, P2000/SK or HK45/45C and you try to fit them into a USP. The USPc parts may fit the USP full-size with the exception of the bobbed hammer, I think. Did you get the bobbed or spurred hammer?Would it make any difference what gun the v1 parts go in? This is an 05 9mm.
Mine is exactly like his, but no problems with mine.hmmm...
Just a thought. I think the sear axle needs to be flush on the right hand side of the frame. It looks like yours is popped out +1/32"....could this be causing the drag?...
Other than that...I got nothin'!