Im pretty sure that the rebooting is from a non compatible radio/rom combo..
Just go into bootloader.. power+camera+reset...hold that until the rainbow screen comes up. Connect to pc and flash an official sprint rom....Active sync wont see the phone but should still update from what I understand.
That will update the radio and rom to the latest release. Since your on sprint let the customizations run at least once. Boot it up and then flash to dcd's rom.
Shouldnt have to unlock again as long as you unlocked with olipro 2.40 or nueSPL 2.47.
Pretty much all the newer roms need a gps enabled radio to work right. Though you should have the latest radio which right now is 3.42.xx anyway to get the best reception and gps locks.
Get the sprint update from the HTC site here.
http://www.htc.com/us/SupportDownloa..._id=75&cat=all
Good Luck