Hy Meyer, 350s have a "nylon" governor drive gear, which tends to fail, with no governor pressure the tranny will not shift up. the governor is at the rear of the transmission, under a stamped steel cover retained by a wire clamp I can't remember which side it is on. If you pry the clip off and take the cover off you should be able to pull the governor out of the transmission, the damage to the gear will be obvious. You can replace the governor with a rebuilt one, but the way I understand this problem, a bushing in the rear of the transmission housing or tailshaft housing has worn, allowing the output shaft to put pressure on the governor drive gear, wearing it out, so mearly replacing the damaged part will only give you a short lived repair, hope that helps.
