Truck feels weak when towing/hauling. Suspect something is causing power loss. - hi everyone, im new to the sight i have a 2002 hd 3/4th with 6.0l. when daily driving ...

hi everyone, im new to the sight i have a 2002 hd 3/4th with 6.0l. when daily driving it feels fine maybe a loss of power but not enough to tell. well the other day i was towing 3 fourweelers. 700cc 750cc 1000cc. and a light racing 800cc. well it feels fine on flat roads but going up hill even in tow haul mode it struggles. like has to go down to 2nd gear to make it a normal him for georgia.

i bought the truch from a family member and i know it hadn't been driven too much at all maybe once a week for two years.
i have changed the fuel filter and it got a little better mpg i think.

since i bought the truck i have flushed the ratty. 2 oil changes with 10w oil. every other fill up i use the nkg 44 from the car dealerships to clean the fuel system. replaced spark plugs and wires. stock intake and exhaust and changed the air filter

i was just very disappointed that it felt so weak with that little of a load.

Do you have a check engine light on? you changed the fuel filter did you check fuel pressure while changing that? How many miles? and possibly a fuel pump? other wise possibly coil pack goin bad! Or possibly a O2 sensor or mass air flow making it run lean.... have you noticed any difference in exhaust smell? the sensors may be just starting to go and not quite enough to trigger the light! There is a ton of different options i would recomend hooking it up to a diagnostic to and running a few tests see what it comes back with.

Keep me up dated

no there isnt any service light on. it smells just like water lol it runs really clean or so it seems. i had the fuel filter done by the gm shop and they didnt say there was a problem with pressure. would there be any codes to check if the light wasnt on? but i was correct that any hill it has to go up to keep it at 70-75 with a load it has to jump down to 2nd. but with no load it is fine at 2k and just over doing 80+ i have 35s with 16 in rims i know that would have something to do with it but not that much.

With some diagnostic tools they will have a diagnostic program that will just chart the engine for a given period of time and then compare them to what they whould be running

should i take it to the dealer?

so i took it the dealer and they drove it and they said it felt good and they checked for codes and it didnt have any at all. so i took it to auto zone just in case they said the same thing. anyother ideas?

Doesnt that bite your ass that when you know there is a problem with your vehicle and you take it to the dealership, they run all their tests and they cant find it. you get halfway home and it starts doing it again!

Did you check for vaccum leak? check all vaccum lines for pinholes also check your pvc valve.I would also try spraying some carb cleaner around intake manifold & throttle body base you ' ll be looking for RPM rises . Let me know how it going

ok so i looked at all the vacume lines and i couldnt find any holes but i can admit im still not sure if there are any or not. is there a better way to look then with a black light?

i will spray the throttle body when i get a chance this weekend. i can keep it on right because the stuff is quick drying.

what pisses me of most is that the guy at the dealer drove the hell out of it which i try not to do cause i have like 1200 tires on it but he said it felt fine to him. and that he was shocked that it was taken such good care of and that the tranny would shift down to 1800 rpm in over drive at 65 mph and still have the power to pass without down shifting or putting it in tow haul mode. i liked to hear all that but it doesnt feel like 300hp to me

If the vaccum lines look dry rotted & cracked replace um.For the couple of bucks vaccum line cost at NAPA & the little time it takes to replace them its worth doing even if its not the problem you'll save yourself headaches down the road.
You never mentioned how many miles you have.
You need to have engine at normal operating temp to really get a good test with the carb /throttle body cleaner , it dissolves rather fast & leaves no residue.
Im 85% sure its a vaccum leak.The other things to check would be incorrect spark plug gap,pvc valve,& old/ worn or incorrect level of trans fluid will give you lack of power under load also