your first rebuild?
sounds like serious pressure loss.
The B&M shift improver kit may have listed the check ball locations incorrectly or you looked at the wrong year for your application?
TV cable would not affect reverse since line pressure is raised by the low/reverse boost valve.
there are many things that could be wrong.
Check the assembly of the boost valves... often the DIY folks install them backwards or miss the snap ring groove .... then the boost valves blow out of the bore
Dont worry how old you are... it is the mileage on your body that adds up.