when truck is cold the check engine light comes on and transmission (automatic 4l60e) does not want to shift and when it does it shifts HARD. checked codes and came up with code 12 throttle position sensor, which I replaced to no avail...same problem. now truck dies at random while driving down the road, it will usually start back up, but is getting more frequent, some times have to let it sit for a while before it will start again. Is there a way to check if fuel filter is plugged? Engine is 5.7L TBI.