Dropping out of overdrive ?

My 2000 Dakota Quad has developed a problem of dropping out of overdrive when I start backing down from 70mph, at 63mph it lurches and rpm jumps from 2000 to 3000. Only way to avoid lurch is to manually take out of overdrive and use in drive.

Truck sat for 2 weeks at dealer for painting, when picked up check engine light was on. dealer said to drive it a bit and if light did not go out ,bring it in and he would "reset" it. Don't know if this was related but truck ran fine before. Any ideas would be appriceated. Thanks

go back to the dealer and have them find out why that light is on. I'm willing to bet that it's either a bad output speed sensor or throttle position sensor.