Here are the steps I have successfully used many times to upgrade my xv6800 to the new radio and a custom ROM.
1) For good measure, perform a hard reset by holding down the 2 softkeys while pressing the reset button then press R
2) Just in case record your MSID, MDN, and if you can see it A Key from the PST. You can get there by dialing ##778 Send and using 000000 as your code (I've never been able to see my A Key)
3) Install
Olipro 2.4 bootloader (during installation of the bootloader, after disconnecting and reconnecting the cable from your phone, the RUU instructs you to make sure you have an ActiveSync connection. Ignore this, it is not necessary.)
*When complete be sure to disable USB in ActiveSync to get out of the bootloader (File -> Connection Settings -> Uncheck "Allow USB connections") Re-enable this before the next step
4) Install the new
Sprint ROM
*DO NOT LET THE SPRINT CUSTOMIZATIONS RUN!!! When the flash is complete and you arrive at the Welcome screen it will ask you to tap the screen to proceed, DO NOT PROCEED ANY FURTHER. If using DCDs kitchen you can proceed to flash from here. I can't speak for others although I believe they will do the same.
5) Finally, install the custom ROM of your choice. I am successfully using DCDs 3.0.1 without any issues.
Things to note:
1) I never let the Sprint ROM boot up and run the customizations
2) I had the slow signal aquisition issue so ran *22802 then hit End as soon as it connected
3) I also re-entered the MSID and MDN
4) After performing steps 2-3 I no longer have the slow signal issue
5) No A key was necessary
6) I never had to run *228 to OTA program (in the past programming with *228 has reversed the effect of re-entering the MSID and MDN)
The theory is that the Stock Sprint updater copies your PST settings out before the install then restores them post-install. This is why I never needed to dial *228 or re-enter my A Key
GPS is running great
Not sure about Rev A, still need to tether and test
If you have suggestions on ways to improve this guide, please let me know.