I've been having an issue with my 84 Eagle Wagon and downshifting while pulling large hills at highway speeds. When going to climb over Vail Pass or the Hill to the Eisenhower Tunnel(I 70 Colorado) the Eagle will lug a little bit, give her some gas and she downshifts into second gear at a VERY high RPM. If I try to keep it at 40-45 it will shift back and forth between 2nd and 3rd without stopping so I manually shift into 2nd and cruise over the top at 35MPH to keep the RPM's down. The 258 definately has the power to lug the car over the top of the hills at 65+MPH, it just takes more pedal. She also did this going over Monteagle in Tennessee and some other big east coast hills so I don't believe it is an altitude issue.
The trans is the factory original 215K mile trans and seems to work flawlessly other than this issue. Any way to bypass the kickdown switch like with some sort of button or switch just until I'm over the hills? Like I said she's got the power but the kickdown just seems to be touchy on the hills.
Thanks for the help!