"90 F-250 4X4 351w 5spd. When I first start out and it's warmed up but still somewhat cold, I can rev it to 4 grand and it launches pretty well. After it gets really warmed up or it's a hot day it'll buck & cut out. It runs relatively cool (< 1/2 on the gauge) though I've got a 180 or 192 thermostat. It runs well @ at steady state but not for a load or speed. Most of the sensors are new. Where do I go next?

 

Check for codes and fuel pressure. Test the pressure when it is running well and when it is stumbling. You need to determine if spark or fuel is dropping out.

 

Thanks, I did have some problems with fuel when I did the conversion (it was a 302). Changed out the regulator and that seemed to help. Maybe it's crapping out again. I'll change the coil too.