Hey fellas-new here. I will introduce myself before begging for advice.My name is Matt and I am 26 living in British Columbia Canada. My truck is a 99 2500, only upgrades are a 4 inch exhaust, Raptor frrp and a fuel pressure gauge.

Now for my issue-the truck runs great except for when I am on the highway in overdrive, it gets pretty weak for power and although she will accelerate on level ground if I try to go up a long grade she will slow down until the truck downshifts.

Also If I press the pedal to the floor the tc does not unlock.

Now, with overdrive turned off none of these issues happen, truck runs great and zips up hills without issue...I am far from mechanically inclined and really want to get an idea for what the problem is before I get raped at a shop....Hoping its an easy fix(I can dream can't I? Lol)

 

I should also add fuel pressure remains normal during this. Pretty much all of the above post can be put in to saying I have no power in overdrive