My 88 mustang starts right up no problem stays idle I can rev it up still no issue but on the road it it runs real rough especially from 4th to 5th gear and shakes another thing I have noticed is when I let it sit for a few weeks I take it out for a spin and it drives great. I took it to a shop and they said it's not my trans I already know that I had the whole thing rebuilt this past summer changed the fuel filter cleaned the maf Also it feels underpowered any ideas