bad stumble in overdrive

[Sovereign]

My truck has started running weird. When it shifts into overdrive, it starts to stumble like there's a missing cylinder. It feels the way you'd expect a manual transmission vehicle to feel when you've selected too high of a gear. It's fine running around just in drive. I even floored it going up a hill in drive only without issue. Still slow as dirt but runs smoothly. I was afraid it was an engine load issue and maybe the carb needs to be rebuilt since I don't drive it much and use regular gasoline with has some ethanol in it. It seems tied into the transmission though. I have adjusted the TV cable. I also recently finished installing 3.73 gears. The truck did not have this issue with the 2.73 gears. Could be just coincidence. Are there are transmission changes I should consider or needed to do when I changed to 3.73s? I'm not interested in performance with the truck. I haven't had a chance to investigate anything yet. Does anyone have any suggestions on what to check beyond the basics like plugs, plug wires, timing, etc?

The distributor appears to have been changed to a standard HEI unit. I've removed all emissions valves and solenoids. All vacuum hoses are good and unused ports capped. All of that has been done for a bit. This issue is new.

Thanks