Transmission won't upshift

[Mike_82_Shortbox]

Hi, guys and gals! I can't believe it's been 8 years since the last time I logged in to this Forum!

Well, my transmission started acting up. It won't upshift or downshift properly. This happened quite suddenly one day after I stopped for gas, then seemed to fix itself, and then a few weeks later stopped shifting properly for good.

I haven't been driving it for about a year, but the other day I had to use it, couldn't be avoided.

I found that if I left the line at around half throttle, the trans will upshift to 2nd at about 35 mph, and to 3rd at about 55 mph, just as if I was punching it into "passing gear." It never shifts to 4th, and on stopping, won't downshift to 1st unless I select Neutral, and then back to Drive.

The trans is a 700R4.

Any ideas what might be wrong?