If you said that it runs smooth until you load the engine, that sounds like an ignition issue to me. Internal derangement doesn't come and go.

Have you had the plugs out yet? Pull them and run a compression test. Check the plugs out good, make sure they are okay, and that there is no oil or water in the tubes. Also, smell the plug wire boot to see if any smell electrically burnt. Arching from the boot to the tube is common. It usually happens under load and can be tough to find, but leaves a very distinct smell.

Make sure that the CEL lights up when the key is switched on. If not, then I smell a rat. If so, switch the key on and off 3 times leaving it on the last time. You should get at least a couple of normal codes.

Keep feeding us info and we may just be able to work through this.

If you want to, you can PM me and we can get together on the phone.

Dave