Sounds like an electrical issue to me. It could be the speed sensors or the wires connecting. You can try inspecting the wires, connections, and contacts, and also test the sensors, or just replace the sensors and wires they come with.
Also p0708 is range switch code:
(DTC P0708 TRANSAXLE RANGE SWITCH - HIGH INPUT)
You may just need to replace the transmission range switch, also called neutral safety switch.
When an error comes up you get P1529 (requests check engine light to come on). Due to certain error codes the TCM will go into safety mode not allowing to shift into 4th gear. That is likely the issue there, but see below.
Last edited by jbob; 05-25-2012 at 05:10 AM.