I'm not sure if it is a torque converter lockup issue or if the engine is missing thanks to an electrical problem or what.

I first noticed the stumble in overdrive, 1500 rpm, about 50-55 mph with just enough throttle to maintain speed. It feels like the truck is going over heavy gravel, but the pavement is smooth. Downshifting and maintaining speed smooths it out, as does adding more throttle input. The engine feels like it has normal power except for the stumble.

The check engine light is not on (but does work). I have seen these codes:
P1229
P0700



On the way up the pass this afternoon it seemed worse: it occurred in a wider range of parameters (RPM, speed, gear, and throttle input).

Transmission fluid is clean and clear; it gets drained/filled with new screw on filter every 25K or so. The truck has about 253K miles on it. A few months ago I had some electrical issues that would drop the engine into limp mode, but some fresh wire loom and pinching injector pins seems to have cleared that up.

It's my work truck and sees daily use. The Benz is nice to drive around, but I'd rather not put all my tools in the back seat. The devil on my shoulder is telling me to start looking for a newer truck...

Thoughts?