Just a couple weeks ago I was dealing with the same issue you are now.
Any kind of load, and the engine would bog and miss. 4th and 5th were the worst. Low RPM was very evident, which was never a problem before especially since I put the 4.10's in.
It turned out to be a coil. But it took a while to figure out because it would not throw a code. No matter how bad I got it to bog or miss, it would not throw a code. So I bought a coil knowing that these engines are bad on coils and kept swapping coils until I found the right one. Turned out to be cylinder 7. It drove better instantly. It threw no misfire codes, had no arching marks on the boot, and ohmed out completely within spec.
I'm not saying this is your problem, but your symtoms describe my issue to a T.
Any kind of load, and the engine would bog and miss. 4th and 5th were the worst. Low RPM was very evident, which was never a problem before especially since I put the 4.10's in.
It turned out to be a coil. But it took a while to figure out because it would not throw a code. No matter how bad I got it to bog or miss, it would not throw a code. So I bought a coil knowing that these engines are bad on coils and kept swapping coils until I found the right one. Turned out to be cylinder 7. It drove better instantly. It threw no misfire codes, had no arching marks on the boot, and ohmed out completely within spec.
I'm not saying this is your problem, but your symtoms describe my issue to a T.