Subaru Outback 05 Limp Mode

I have been battling a big boost upon acceleration at stoplights for approximately 6 months. Now twice I have gone into limp mode and the tech reads:
PO700 (Transmission) and PO731 (Gear 1). I just turned over 190,000 miles but only purchased it a year ago. Any thoughts as to what is the problem(s)? How costly SSS are we talking? Please “dumb” it down guys…I’m a scientist, not a mechanic! Thanks!

I’m presuming you have an automatic transmission, right? If so, the first step is to verify the transmission fluid level is correct. If that’s ok, the next step for most vehicles then would be a proper transmission service, dropping & cleaning the pan, replacing the transmission filter, and re-filling with fresh fluid. If all that doesn’t fix the problem, you may be looking at a transmission rebuild. But you might get lucky & just need a faulty sensor or actuator replaced. A good transmission specialist could easily tell you.