I have a 2009 Chevy Express 2500. The van will shake when using the brake between 40 and 60 mph, fine at all other speeds. So far I have had new tie rod ends(innner and outer), 4 new rotors, all new brakes, new rear calipers, new shocks, new sway bar ends, new idler arm assembly, new tires (balanced and aligned) I don't feel it in the peddle, it's far worse downhill or pulling a load. Every mechanic just tells me new rotors. I have a hard time believing the old ones I pullled off have the exact same defect as the replacements immediately after replacing them, especially at only between 40 and 60 mph. If you have any suggestions I am open.

 

Recheck the tire balance

 

upper ball joint.
Check all front end for wear.
Check caliper bracket to make sure the caliper floats properly, and does not bind.
Do you feel it in the steering wheel?