The truck was working perfectly up until I stopped by a local Subway. When I left the parking lot, I had the "O/D Off" light show on my dash when I never even touched the overdrive. When I turned onto the road I noticed my RPM's was going up to 2500 when I was going only 20 mph. I decided to go 30 mph to see if it would shift at a high RPM and it went up to 3500 RPM's. Clearly, something is wrong at this point. I continued to drive 20 mph all the way home (7 miles). As I turned down our neighborhood driveway, the "Transmission Temp" light appeared on my dash. The next morning, I drove it down to our family mechanic and it started shifting much better the fallowing day but the fact that it did the prior is my concern. I first was considering if it needed an oil change due to smell cooked oil after driving it. I bought this truck from a 3rd party several weeks ago and so I am unaware of when it was last serviced. Any suggestions?
It won't hurt to service the trans. However, I don't think that was the cause of the problem. Has the OD light since gone off? By any chance, was the computer scanned for possible transmission trouble codes when the light was on? Is the transmission now shifting normally?