While driving especially while im stopped it starts shaking and the rpms start to shimmy up and down. Now today and yesterday it will make a two or three popping noises from under the hood. When im driving along it only has around half power then starts accelerating normal.It doesnt do this all the time its speratic. What could cause this, i believe it could be my cat because it stuttered awhile back and the engine light would blink saying it was the cat.I dont get a light now when it happens so im steering away from that possibility. It has the 4.0, auto and 63,000 miles and the only mods are a thrush turbo exhaust and a homemade cold air. Any help would be awesome.

 

Bump

 

any clue please im worried about possible transmission crapping out.