in a 02 2500hd that has a mis in it when going up hills you can feel it missing it runs fine in all other situations onl when going up hills i have changed plugs and wires and fuel filter and air filter and put seafoam in the gas tank, not getting any codes,9.5 gas mileage what could be the problem?it has 52000 miles on it, thanks rick

 

try a little octane booster in the gas, it might be having a detonation problem just an idea...