Ok so yesterday I had a 3" dp put in my truck. I put my a stock turbo back on cause I couldn't light up my big turbo but now with this dp I've lost a total of 30 pounds. Before I could it 30 now I only get a max of 12. I'm gonna check make sure there's no leaks anywhere but I was wondering if the bigger dp is the problem & that's why I couldn't get my other one to light cause of the back pressure on it.

 

The downpipe has absolutely 0 to do with your low boost. You have other problems