I've got a 2500 6.0 ltr short box ext cab, some old guy had it before me and just drove it on the highway with a topper, it's in excellent shape, doesn't burn oil and gets 18 miles to the gallon on the highway with a k&n set up, not just the filter. But, ever so recently the SOB shifts on me when I goose it on the highway to pass someone or to blow some Ford's or Dodge's doors off! It spits and sputters and farts and has a delayed up shifting deal. It only happens when I'm going anywhere from 25 to 35 mph and goose it, it accelerates beautifully, but as soon as the f*cker hits 5000 rpm it shifts on me, I let off the gas a little and it shifts just fine and everythings ok. It also happens when I'm in highway gear and I goose it does the same thing when it hits high rpm, then when it shifts into higher gear, it used to sound awesome, a fine tuned engine shifting into another gear with my dual cat back exhaust, that nice flowing exploding sound. But, now it shifts out the exhaust when it shifts and I'm really on it. This is my complaint and I'm pretty pissed off about it. I have no idea what to do. I like this pickup, good solid and beautiful, I want to fix it, got a lot of ideas where to start, want to start cheap and work up, but don't know what to do yet. Anybody have a similar problem and fixed it? Any info you got would be very much appreciated. Semper Fi!