Viper mpi turbo straight pipe

I have a mpi Yamaha 190 kit on my 2015 viper. I built a straight pipe for it and I'm seeing it over rev on take off twice. Them it spikes 10 psi and drops to about 8 psi. So for now to make sure the ebc isn't messing up. I'm putting the stock muffler back on to test. Does any one have experience with this. I'm sure I will have to re-clutch. And it's easy to lower boost with the waste gate. Just looking for info on clutching or experience with a straight pipe. Does the loud mpi muffler cause the same thing? I am thinking a little back pressure might be helpful.

I it the stock mm ****er back in and finally got back out today. Everything worked properly. So g of ING to have to try again with the rod out a couple turns. Just wanted to make sure nothing messed up while it sat all summer.