my 83' 300D has a transmission with a mind of its own.. from any gear, when you go to put it in reverse, it acts like it has to think what "R" means.. it normally takes about 4 seconds to shift, after the shift selector has been moved. as i sit there, ready to back into a parking spot, people are starting to look at me like i dont know how to drive.. please help!

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1983 mercedes benz 300D turbo diesel.
pyrometer, boost/vacuum gauge
exhaust dump pipe
turbo- 15 psi boost. 25 psi capability
disconnected EGR