'03 duramax performance question

We have an '03 Chevy 2500HD with the duramax and allison transmission. My question is, when pulling in the mountains with tow haul on and one presses on the go pedal, isn't one supposed to get a steady increase in power? When I mashed the go pedal, my truck did not move on up the slope. It slowed down with the increase in upward angle while the rpms stayed the same. When the speed got about 10-15 mph slower than the 65 mph speed I was trying to maintain, something kicked in-the roaring began and power came up to match the "floored" pedal. It happened even on small hills. It seemed to be all or nothing. Is that normal? Am I doing something wrong with the driving? Should I be looking for a mechanic? This question was also in the Trailer Life magazine. It sounded very similar to mine. Any replies will be appreciated.

question is, when pulling in the mountains with tow haul on and one presses on the go pedal, isn't one supposed to get a steady increase in power? When I mashed the go pedal, my truck did not move on up the slope. It slowed down with the increase in upward angle while the rpms stayed the same. When the speed got about 10-15 mph slower than the 65 mph speed I was trying to maintain, something kicked in-the roaring began and power came up to match the "floored" pedal. It happened even on small hills. It seemed to be all or nothing. Is that normal? Am I doing something wrong with the driving? Should I be looking for a mechanic? This question was also in the Trailer Life magazine. It sounded very similar to mine. Any replies will be appreciated.

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