I am thinking that the tuner is not doing it, but i am not 100% sure.

 

I have the same surging problem and fuel pressure does not change. Did the APPS reset and seemed to make it worse so I'm thinking that the APPS is on it's way out.

 

I did the same reset the apps and nothin doin while i had it apart i "swept the apps with a dvom and didnt see any voltage drops stayed steady all the way through. seems to do it more when hot for me anyway idk the apps are around 250-300 from napa if i remember right. I was going to get one, thought it was going to be the same as a gasser tps 50-60 so i would just throw one on priced it and decided no not yet till i confirm the prob so IDK what to do either.