When you pull the solenoid take a little magnet and see if the valve will come out. then see if it has a spring around it or in it . coans brake valve has a spring in the back of it and mine has a spring around it. I heard here that some don't have springs they work off presure. I.m not very smart on trannys but I will try to figure them out. clean off your valve when you take it out and check the spring tension. it sounds like my problem. the same thing happened to me last week @ a race just a little reverse and no brake. when I hit the Brake button and floored it and we went red and flew down the track. that was the 2nd solenoid. so I put the new coan in it and now it works perfect. I hope this will help you I know how agravating this can be. Good Luck
Andy Byrd