I got force-fed Gingerbread by Verizon last weekend, It worked great most of the day (EXCEPT for wireless tether) until the battery died. As soon as I installed the spare battery, it started bootlooping on me. I researched it and it appears that I did the same things you have tried. I tried countless SBF files, all either failed or said they were successful but the bootloop continued. After about 5 hours of this, I found a blog that said there was an issue going from a rooted Froyo directly to Gingerbread OTA and suggested that the only way to recover from this was to restore the phone to factory settings, then install Gingerbread and my apps, then root the Gingerbread install. I booted to recovery mode, restored the phone to factory, let Google recover (Most of) my apps and contacts, then upgraded to Gingerbread without issue. I waited 24 hours to ensure I had no other lingering issues, rooted the Gingerbread install and then my root apps. I'm not sure what phone you have but this was the only way out that I could find, I hope it helps you.
These are the steps to boot your Droid 2 phone into Recovery Mode should you need to.
Perform a hard reset on your Verizon Motorola Droid 2 if you wish to wipe all the
data from the device.
From device startup
1. Turn the Droid 2 off. If it’s frozen and you cannot turn it off, pull and replace the battery.
2. Open the keyboard and press the
X key while pressing and holding
Power. The device will power on. Keep holding the X button downuntil a white triangle with yellow exclamation mark appears.
3. Press the
Search key on the keyboard
(magnifying glass).
4. Use the
Volume Up and
Volume Down buttons on the side of the phone to select the
Wipe data factory reset option. Use the
Camera key to confirm it.
5. Tap
wipe data/factory reset then tap
OK.
6. Highlight
reboot system now is highlighted then tap
OK.
Here is the link to where I found the instructions to Hard Reset the phone:
Droid 2: Hard Reset | Technipages
There are similar links on the bottom for other phones, if you do not have a Droid 2.
Good Luck.