I have a 2005 h2 with 53k miles. Truck drove great since I got it 3 yes ago but 3 weeks ago it felt like the truck lost power. Now to go same speed as before I have to press down on gas more. And because of this the engine is louder and rpms get over 2k rpms to get to 40mph then of course it shifts and rpms gets down under 2k rpms. I took it in to hummer dealer and took mechanic for a ride. He connected his diag tool and no error codes came up. He said truck rides like it should. I know darn well it's not driving like it used to. Other symptoms: truck slows down quicker now, truck has no pickup, even if your at 40mph and press gas, it seems like it's struggling to get to 70mph. Could it be the spark plugs/wires?

 

it sounds like your 4 wheel low is selected. check it.

 

Thats not it. I took it back to hummer dealer and test drove it with head hummer tech and service mgr. They say it's running normal but I know it's not. Huge difference in pickup and accelerating. I Also changed the mass air input sensor but that didn't help at all.

Just pressing gas pedal slightly to try to accelerate from 50 to 60 the rpms go over 2000rpms, that is not normal for my truck. Engine also is much louder now and feels like it's struggling. Hummer dealer connected the diagnostic machine and showing no codes.

Anyone have any other suggestions?