ok i have a 2003 z71 silverado its got the 5.3l in it with 4l603 transmission. ive been having issues for quite sometime now with it losing rpms and dying at ide speeds. such as when im comming to a stop light or sign or go to park in a parking lot. the tach will drop and the truck will fall on its nose an dye. ive done as suggested by mecahanics and the chevy house cleaned throttle body and MAF and the air intake filter. changed plugs and plug wires changed the fuel filter. and this problem still occurs ive heard it could be the drive by wire throttle body. or could be a leak in the intake gasket now ive priced a gasket and its about 70$ and i have a chiltons book. but is there a way i could test for this without a smoke machiene or ? could someone help with some issues here?