Tolaran

My bike, a 02 Suzuki DL1000 V-Strom, has developed problems that neither I nor my regular shop can figure out. During early summer the bike developed a flat spot where it just seemed to run out of steam as if it was starving for fuel. After playing with the throttle she'd settle down. Took her into the shop and they couldn't figure it out. The rear cylinder is misfiring. A tune-up, fuel injection system flush and new plugs helped but didn't cure the problem. Took her to a Suzuki dealer to put her on the scope but that didn't give us any more information about what was wrong. I rode her up until late November and had to park her because she was getting progressively worse. The bike is constantly backfiring through the TBs, it has no power (feels like it's starving again), and mileage has tanked (down to about 25 mpg instead of her usual 45). The plugs are clean, spark is good, fuel is good and it's running lean (no fouling). She's been a great bike up until now. HELP!!! Any suggestions would be appreciated.