My daughter has a 86 accord that as of yesterday started downshifting while driving. it is also not wanting to upshift while accelerating. This only happens after it has warmed up. i have not been able to find a vacuum leak and tranny fluid is at the top of the band. any ideas what i should be looking at?

 

I have been told there is a temperature control vave that might be causeing this. Any body got any ideas? HELP!!!!!

Where is it and how can i tell