START NO START

Have a 69 cuda with auto trans, have replaced the safety netrual switch in the trans when had the trans. rebuilt, from time to time will not start in park, need to shift to netural to start, seems like when cold 1st start it is ok but when warmed up, gives me the problem have adjusted and readjusted the shift linkage a few times and made sure to tighten the set screw good so it does not move but still acts up any thoughts ?