Levi Henson

Just bought a 2003 GMC sierra 1500hd 300k on the body but paperwork provided from the owner says it had an engine swap with 140k on it. Sometimes pulling hills ill lose speed and have to floor it to kick it down to gain speed. engine has good compression and other times performs fine. MIL/CEL never comes on so I assume there isnt any codes to read. What can I check? the exhaust from the cat back is like swiss cheese which I will be replacing tomorrow but I dont think that would cause significant loss of power would it? Manifolds and stuff are fine no leaks.

Just bought a 2003 GMC 1500HD 4x4. The truck seems to drive fine shifts well through the gears no slipping 4x4 works. But it will not manually shift down into 1st gear. I have a hard time telling if its shifting into 1st in "D" because it has oversized tires and a big heavy bumper up front, it feels a little sluggish off the line compared to my 04 escalade but not crazy given the Esky is AWD. I searched around and couldn't find anything regarding the physical inability to shift into 1st. Going to disconnect the linkage this weekend and see if I can manually go through the positions from under the truck. Is there anything else I should check?