Trans problem with CEL

[JDMdreamz]

ok well recently my cars been shifting funny first to second shift harsh then sliping intwo 3rd and the car dosnt shift into 4th at all i can go up to 100mph at like 6500 rpm and it won't shift i have a check engine light p1720 iv been told it could be the drop resistor has anyone else had this problem

[maxhopper]

The drop resistor would explain the harsh shift, but not the slipping, or the no 4th gear problem. You can try to unplug the drop resistor and see if it gets worse, or if it has no effect. If it has no effect, I would replace it. Your other issues sound like and internal failure.

Have you been driving it in this condition long?