Slant six still doing the same thing?

i ve recently discovered that the gaskets on the carb were allowing air inside which i guess causes the engine to stall when i press the brakes in forward or reverse gear(manual brakes btw) which puts a load on the engine so i replace the gaskets but it still does the same thing now i got another problem the kickdown stays engage on takeoff and if you release the gas petal the rear end jerks which i knw isnt good for a trans too. i need to know what can be the problem of the engine dying when the brakes are applied in gear and solve my kickdown issue. the engine runs fine in neutral and revs great but in gear when the brakes applied it dies. can it be the timing, carb is too damage beyond repair which i hope not, or what can be the problem?