Be Careful! If you depend on the car for daily transportation and don't have 1000+ cash available for repairs, then just don't power shift.
I say this from experience. The shift forks in the T45 are weak and break after repeated power shifts or missed gears. Replacing the shift forks requires the transmission to be REMOVED and pretty much everything inside disassembled and costs over 1k$. The forks are weak cast aluminum and not very strong... especially if you are trying to power shift with worn syncros, which is typical for more than about 50k miles.
Anyway... I started with low rpms. Try some power shifts from 3rd to 4th at 1500-2000rpm. You won't be in danger of breaking the tires loose and the lower revs give plenty of time to recover with little consequence. Timing is everything. Then, work the rpms up, keeping in mind that it takes more finess and strength at higher revs. Unless you have a new transmission, your syncros are probably worn, and will cause significant extra resistance when changing at high rpms (and danger for breaking shift forks). In fact, I can't power shift at 5500 or above because the syncros just can't keep up.
Power shifting is great fun and the only way to post up good times at the track with a stockish NPI. Just be careful. It is pretty easy to get sideways on a hard 1-2 shift. WHEN you break a shift fork, I highly recommend installing forks from Hanlin. They are supposably stronger. I've been running them for a while and I'm pretty happy with them.