If it's an 8" converter(which is what I think you said it was), then that's about where it would stall.
It can be tightened up, but I think in the long run you'd be better off leaving it as is and installing a longer duration cam( and aftermarket rods).

The 8" behind my 383 stalled 5400...... And it worked great!!

I'd start working on sorting out the 60' issue...... Less stall won't really "fix" whatever the problem is there.