I just got back from a long weekend trip.
On the way up to the lake all went well, although I did use caution and dropped a gear or two up the big hills. Kept the revs up and easy on the throttle.
On the way back I made it halfway home, this time driving normally without dropping gears on the hills and it occurred once on a long hill.
I pulled over, plugged in my code reader and same code again, P0087. I reset it and drove carefully the rest of the way home without issue.
Temperature was quite warm - in the high 80's.
I am going to change out the rubber lines by the transmission and see if that helps. But I won't know until I hitch up and go up a long steep grade towing.
Best to try the cheap stuff before getting into the more costly items.
Thanks for all the help everyone.
