I have a 3000 9.5" non lock and it shift like this (leaving it in drive and it shifting on its own):
At normal take off 1 to 2 is 4200rpm and 2 to 3 is 5000 rpm
At WOT 1 to 2 5500 rpm and 2 to3 6000 rpm.
You should shift higher , is your tranny oil level correct ??
Do you have a shift kit.
Try appling your brake( use line lock if you have it) running up your stall just before the tires break lose( which should be around 1800 rpm ) then just floor it this is called flashing , it should shift higher then what your shifting at now.
Good luck !!!!