yeah..... dont do the 1-2-1 shuffle! Its very bad for the trans... built or not. Just leave it in drive, put it too the floor and let the trans shift on its own. Test have shown that the 1-D-1 shuffle isnt any faster then letting the tranny do the work.
but like everyone else... sounds like your in 3rd gear... not 4th. Try adjusting the shifter cable at the transmission, it may be to tight to hit 4th gear (OD)
oh and another thing, with that much gear and a performance trans... youll want at least a 26" tire for optimal performance.