Please help me solve this mechanical mystery

[ubtripn]

I hooked up my overdrive last year on my 700R4. (Did not use the kit, just wired it to activate when I hit 4th gear. (Poor mans solution.) So when I am accelerating and it is about to shift into 4th it does so then 1 second later drops an additional 2-300 RPM's.

I drove it for 3 month and 65 mph was 2100 RPM. Overtime it changed and 65mph became 2500. My idle in park jumped to almost 1500 and it became 1000 in gear.

This morning it switched back after many months. 65mph is now 2100 RPM's again and it idles in gear at 700, 1000 in park.

What could cause this change?

Thank you for the help all.