THe transmission used to downshift through each gear successfully but now I can tell something is wrong. When braking( downhill or not) it no longer downshifts and engine brakes through the gears as it once did. While braking, the revs drop to just above idle even when at a decent speed(30 mph or so) and does it's little blip when dropping to 1st then falls to idle. It seems to shift just fine on throttle but the sudden lack of engine brake without any CEL light has me worried. Checked the tranny fluid the other day, color is bright(tranny was replaced about 30k miles ago) and no grainy texture on the dipstick. It almost seems like a need to purchase an obd reader but what's the chances of no code being pulled?