Engine/Transmission (1998.5 - 2002) FGreiss 99 2500 TD Alt. not ch. Trans. not Shifting into Over drive.

Noticed alt. not chg. over 11.28 volts replaced Alt. no change, batteries fully charged. Also trans. no bottom end will not lock into over drive. I have already had to deal with interference due to alt. Had My buddy check power train but computer not able to read transmission shifting. At dead stop 1st gear is dragging . If I shift to low Automatic trans. truck moves on like normal 2nd gear not really responding until I shift into drive and we are moving like normal but will not lock into over drive , and using over drive button does not change any thing. Computer or Trans. problem?. Thanks to all that respond.

New day, checked relay like JR suggested, ok now i'm at battery cables grounded but corrison has set in. I miss spoke in my 1st post. My buddy ( transmisson mechanic) could not get his computer to read either PCM nor ECM. He thinks that the battery cables could be a factor, and keep in mind PCM is not talking to alternator, any suggestion's? Thanks.

 

The PCM on the pass side firewall controls both those functions so it's a possibility yours is bad. Some things to check off the top of my head are the main fuse link for the altenator in the PDC on drivers side under the hood. There's also a 20 amp fuse and a relay for the OD solenoid. Swap out the horn relay for the trans relay. You can verify both relays work by honking the horn.
Also trace all wires from altenator to ground. Check all battery cables and grounds for corrosion and tightness.

 

Thanks JR will do