Can timing being off cause plug fouling/intermittent stumbling?
 

Trucks been acting up the last couple of days, so after replacing the water pump today I checked things out. #2 plug was fouled and I have intermittent bouts of the engine stumbling, but then it runs fine for miles. Turns out, my timing was up to about 10 degrees BTDC. Put it back to 5 and havn't had any stumbling issues since. Checked the compression on the cylinder and it was at 145. Think the timing could have been causing the problems?