constant misfire no codes?

my 99 blazer has developed a rather annoying constant misfire under light accel between 1500 and 2300 rpm. it will sputter as if it has a rev limiter. if i press the pedal harder or let it idle it goes away completely. my first checks were cap/rotor since it seems to do this more when wet outside. i replaced all the tune up parts about 20K ago and used quality parts. everything checked out fine.

the part that confuses me is that it will not set a DTC. scanned it and nothing. usually a misfire will cause a SES light. whats stranger is if it does it for more then 30 seconds the lockup converter won't engage for awhile unless i'm in the throttle more. someone told me the TPS is going bad but i've never heard of a TPS causing a misfire. so should i spend the 40 bucks and replace the TPS? i can rule out fuel pressure or clogged cat because it runs fine under moderate accel.