O/D Button then P0770

So I finally took my 2002 Tacoma out of town for the first time since owning it. Its got 223k miles on it. I went up north about ~100 miles a lot of which was uphill. I thought this might be a good time to try that ol' Overdrive button to help get up the hill faster. Well im kind of an idiot and thought it would be a good idea to switch in and out of O/D when I wasnt going uphill... well at some point I turn the O/D on and the RPM obviously lurch forward to 4000-4500 and then my scanner goes into an "RPM Alarm" even though I was no where near redline but it was an abrupt jump from the 3000's to mid 4000's. I turned O/D off and just continued driving as normal.

Well on the way home(mostly downhill) about 30 miles in - my scan tool starts throwing a P0770 code. I would venture to guess this has something to do with all my screwing around with the O/D button while going 80+MPH uphill.

Is this a REAL bad sign of some damage done? Is this a fixable issue within a reasonable cost or is this one of those "I fixed everything and it still throws the code" situations im reading a lot about???