So, my truck has always had this intermittent issue with reverse not working, when it did engage, it worked fine, no slipping. But when it didn't you just had to go to N and back to R and it was in. Well I've really gotten tired of it and while adding an external filter did help reduce this occurrence, it didn't completely eliminate it. A little while ago I had picked up some sea foam and some sea foam TRANS TUNE. I had used the sea foam but left the trans tune on the shelf as I feared it would do more harm than good. I took my road trip this summer and a few days ago I remembered I had bought this stuff. I figured, what the heck.
The instructions said to put 1/2 a can in, run for a little bit then change the fluid. I dumped the whole can in and will be changing the fluid this afternoon. After driving it to school and back I immediately noticed that it shifted better, and faster. Reverse has been working 100% since then! This @!*% really works. I checked the fluid and wow it got darker so I'm going to change it today. I will pick up another can of trans tune, put 1/2 in and leave it for the next 10k before I do another change to fully clean the tranny.
So, if you are having reverse engagement issues I would try this stuff. It will not help a slipping tranny though, only one that is clogged up with @!*%. I took my truck to a well known trans shop and told them what happened, they told me that there is a 90% chance the valve body was plugged up.
http://www.seafoamsales.com/trans-tune.html