4R70W Valve Body Issue?

[cknorw]

I rebuilt my trany 8 years ago, just about to turn 100k miles. My current issue is with reverse. I have a down hill slope out my driveway. When shift to reverse, no problem, engages fine. Coasting down the drive, it seems to go to neutral. When I get to bottom and give it gas to back out (street is slight uphill), I get rev of engine then a bump back into reverse. I can back up the driveway, never loses reverse. Forward seems fine. Twice when cold both times, had a slight bump feel when leaving a stop sign. All shifts feel good, never slips. Fluid level good, serviced in March 2014. Fluid does not smell burnt, still looks like new. Really wouldn't know I have an issue if I pulled forward out my driveway. This has been going on for the last 4-5k miles. Doesn't quite fit the boost valve issues i've read about, but seems reasonable. Any thoughts?

 

[cknorw]

Update... A week ago, I dropped the pan and found the filter in the bottom. The filter let go of the rubber seal (autozone filter). Ive used them before with no problems. Put a new Ford filter in. Now holds reverse down the driveway. No neutral feel. With the filter out, pump lost prime. All is well. Almost 101k miles on transmission.