I have trouble with the 2-3 shift on my SPF also. TKO600 behind Roush 427R. My motor is out and back at Roush for some work, so while its out I'm putting the Steeda Tri-Ax shifter in it. I'm also getting a scattershield, just in case, the 402 headers are going in, and some Olthoff motor mounts. If you have the 402 headers you should be all set.
If you want more horses you can look at new mufflers or complete sidepipes. I've got a set of classic chambered mufflers that need to get welded in too, probalby over the winter.
Oh and I've got a set of MT 325/50-15s in the garage just waiting to get mounted too
Always something to change