You can try third gear but it depends on what's causing it to go into limp mode. The fault codes will tell you that. As a general rule, if it goes into second gear as soon as you shift into drive, even before the car starts moving, it is a sensor or other electrical-related problem.
If it starts out in first gear like normal, then bangs back to second gear during or right after a shift, usually an up-shift, it's clutch pack wear-related. There's an input speed sensor that monitors engine speed, and an output speed sensor that monitors wheel speed. The computer knows how fast one should be going compared to the other one for each gear. When there is a discrepancy, the computer knows there is slippage taking place in one of the clutch packs. That's due to mileage and wear. Years ago we had a year or two worth of sluggish shifts and engine "runaway" during shifts to let us know that wear was taking place and a rebuild would soon be needed. With Chrysler's computer controls the computer makes up for that wear by releasing one gear a little later giving the new gear more time to lock up solidly. It updates those shift schedules continuously throughout the life of the transmission. The advantage is you always get nice crisp, solid shifts like when it was new. The disadvantage is you don't get the year or two of warning that the wear is taking place. One day it shifts fine and the next day enough slippage occurs to send it into limp mode.
If it goes to limp mode while driving and you can identify when it always occurs, you may be able to get around it for a while. For example, if it only occurs when it shifts from third to overdrive under light throttle, you can accelerate more aggressively in third to reach a higher speed, then let off the accelerator pedal and let it go into overdrive with no load on the engine or transmission. Overdrive will lock up solidly within a couple of seconds, then you can continue accelerating moderately, like normal. With no load there won't be that slippage, and since there's no slippage to detect, it won't go into limp mode.
Besides reading the fault codes, your mechanic can use his scanner to read the "clutch volume index", (CVI). That is a set of four numbers corresponding to the number of ccs of fluid it takes to apply each clutch pack. Based on those numbers an experienced transmission mechanic can tell how much life is left in the clutch plates.
Wednesday, September 4th, 2013 AT 6:31 PM