Why does my toyota automatic not always engage kn reverse gear?

I have Toyota townace.for somevtime intermittently its not always engaged into reverse gear. Sounds like spinning perhaps. i rev so hard it only crawls.. its like no engaging. I have in this time prior had rear axle seal redone as it was not done right FRom prev owner work & oil pushed thru to brakes too and they needed replacing. Could this work? Area, have effect cause this? TranFluids look not too bad and levels are adequate... it is getting worse. I do also have a stretched accrlerator cable.. but didnt think this could have anything to do with reversing problem. ..??HELP PLEASE