Trans fail safe mode need help
 

Snap on code 221

It can be anything from serious to just low on oil. Probably helps to explain more about the symptoms and what has been done.

Trans fail safe mode
 

After replacing radiator Trans fail safe mode which causes: speed,rpm,and temp gauges not to work properly also by it being in that mode car takes off in 4th gear .once car resets it's fine then It starts all over again

First thought is that the transmission oil cooler attaches to the lower right (passenger side) corner of the radiator. If the thermostat built into that attachment was damaged or it was someone not connected correctly, you could have insufficient transmission fluid cooling or be leaking transmission fluid there. The on-again off-again nature suggests it is ok when cool, but then triggers fail safe mode once it warms up. Again, perhaps pointing to inadequate cooling.

Have you checked the transmission fluid level?

Did you replace the trans fluid that came out of the hoses and radiator when you replaced the radiator. If not there's your problem. If you did hopefully you follow the procedure to refill a trans, if not there's your problem.

It is possible (and proper) to remove the transmission cooler from the radiator without opening the tranmsision lines, but one never knows if it was done correctly or not. I guess it is also possible the cooler was replaced along with the radiator, which definitely would have required opening those lines.