Engine Missing Mid RPM Under Load

[blk85cj7]

THe CJ is missing as the engine revs under load. Mid RPM range, climbing a hill, in 3rd and 4th gear. If I let off the gas a bit it's starts running better. Once I get the RPM's up the engine moves past the stumbling/missing. I've changed the plugs and the distributor cap and rotor look to be in OK shape. The plugs were crispy but I think that's from me learning how to tune my carb. What should I look at next?
It's a D.U.I distributor with about 7K miles.