Code P0755 - is it possible for it to be low or dirty transmission fluid?

Without any warning, i.E. Noise, slamming into gear, etc. I just suddenly lost my REVERSE. It's a 4 cylinder LE. Code P0755. Possible fixes were suggested:
A/T switch solenoid SS2 or "B" stuck open or closed; component problem (i.E in clutch, brakes or gears)or transmission valve body is clogged, dirty or stuck. Could you let me know what you think and how much it would cost for a repair. All other gears work normally. Would it be safe to drive it to a repair shop? (If I can get the car turned around, lol) I would rather not have to pay for towing.

Also, February 2012 had repairs done to Evap System for codes P0401, P0446. Repairs done replacing Evap control charcoal canister;Vacuum Switching Valve (EGR VSV), Fuel Vapor control Valve and a flex pipe. Approx. 3 weeks ago I heard popping noise and smelled gas (same thing prior to repair in February)and now, approximately only 3 months later) I get another reading: P0442 (no check engine light, yet). Two of the possible problems are: 1. Canister Purge valve is damaged, leaking or failed. 2. Charcoal filter is loaded with fuel or moisture.

I insisted they replace charcoal canister as recommended by Toyota. I am concerned I may have been charged for a new one and labor and it was not done; or hopefully I'm wrong and it may be a defect or another cause. But it seems to be more than a coincidence that I should have the same symptom as before and their repair should have resolved it. Should I take it somewhere else?