Well heck, RunOfLuck, I thought I had searched thru all the posts and didn't find anything specific to the MyTouch 4G. Must have missed yours.

Posted my own after trying all the suggestions for other phones.
As for my status... Finally picked up my car last night and worked with the dealer until I was able to connect. Yay! But it first failed, meaning I was able to pair and connect, but the "downloading phonebook" message wouldn't go away. So, with the dealer's help, I went thru this process:
On my phone, I deleted my call history and the bluetooth headset I already had paired, then powered off the phone. On the car, I deleted the phone and turned it off. Gave it a few minutes, then started the car again and powered my phone on. Turned Bluetooth on for the phone and in the settings made it 'discoverable' (which it does for something like 119 seconds or so). On the car, went to "setup", "phone", and "pair". Back on the phone, I ticked the "scan for devices" option. The phone asked for the validation code (0000) almost immediately. Typed it in and the car spoke "Phone Paired", while on the phone it listed "FORTE KOUP--paired but not connected". On the phone, I tapped the newly paired Forte Koup entry and the car's display read "Kat-MyTouch 4G Connection Complete". Now... we'd already gotten thru these steps successfully once. But when I pressed the talk button on the car this time, instead of displaying "downloading phonebook" on the car's display for an eternity, it asked me for a command almost immediately. Yay! And away we went!
I have absolutely NO idea what we did differently the 2nd time around. Perhaps it's like RunOfLuck suggested--it was trying to download external contacts (I don't have Twitter, but I do have a lot of Facebook contacts) and by restarting the phone and the car, it stopped that process. I don't know. At this point, I don't care.
Thanks for all your help & suggestions, everyone! Happy driving!
****EDIT****
Oh, there's one step in there I forgot to mention. After the connection between the two was complete, my phone displayed a message that said something to the effect of "FORTE KOUP is requesting access to your phonebook" and it gave me an option to accept or deny, and of course, I accepted it after ticking the "always accept" button. On hindsight, perhaps it was this step that I didn't do right the first time. Maybe by accepting the Koup's inquiry on the phone right away, it made a difference. *shrug* Who knows?