voltage drop when in gear

I have been having a problem with the gauge reading around 9 - 10v when i start it then rises to alittle under 14 after about 5 min. then bounces back and forth periodicly. I have redone all main grounds with 1awg wire grinding or sanding all places they touch and the starter relay wire mod to the fuse box. Now I start it it goes to 14v but now when I put it in a drive it drops to 11v and reverse drops to 9v put it back in park jumps to 14v again. I do need to replace the tps but it still runs just has a high idle after it warms up. I took it to the auto parts store they said both the battery and alt are good. Would the c-101 connector have anything to do with that? I'll take all the ideas I can get, thanks in advance