Hello, I have a 1995 Silverado 1500HD 4x4 with the 5.7L engine. It idles good and I can run it up to 2500rpm and it will purr like a kitten. Once I put it in drive and go down the road its real sluggish. I hooked up a 10' x 6' trailer and you would have thought I was pulling a freight train. The brakes are not hanging up. Any idea's what is going on?