your pressure is correct and good for the overdrive 22-1374, when you test and your pressure is at 350,when you shift it in to overdrive the pressure should drop 50 lbs and then come right back to 350,
when you release it out of overdrive,your flange on the rear should spin both ways free,if it doesnt you are stuck in overdrive.No you should not put it in yet, you can tap on the back of the overdrive to release it,or the operating valve is clogged,very small pin hole that is plugged and wont release the pressure,have to take it out,easy while on the bench,take your gauge out,ball spring plunger as well,and then take a magnet and pull the operating valve out and ck the pin hole in it,blow into the valve,you will know if its plugged,the put it back in and retest
Phil