Rattaan

OK, here's the deal. I have a '90 NA with a problem of hesitation/jerking between shifts. The car has done this before and I found the plugs seeming to be the culprit. I have an MSD 6a on the leading coil and my plugs get eaten up fairly quickly(rear rotor more than front in about 5-6k miles). I have the timing set dead on the marks, and have just recently reset the TPS(may need finer adjusting, but did a heck of a job smoothing out deceleration and steady throttle). I'll be changing the plugs here in a few minutes but even after doing these it still once in a while has the hesitation between shifts. Can anyone suggest some other possibilities as to the reason I get this sort of clunk when I let the clutch out on an upshift? Any help or suggestions would be greatly appreciated as it has been bothering me alot lately to have this persistant though intermitent annoyance. Anyone