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I just changed my 4.6L. Now my tranny is starting to serge and buck it won't go in rev. But when I put it in D it started to clunk and buck. RPM would go up speed went down.
Sounds like you might have linkage problems.
Reverse is a mechanical function that has no solenoids involved except the pressure control valve.
It could be a blown fuse #23 pinched harness etc..
Otherwise there nothing solid to go on at the moment until you find something positive.
Good luck.