Race car mystery-Help us solve PLEASE

I'm going to try and keep this short as possible but we have a very weird issues going on,67 valiant,727 trany,ladder bar suspension,New msd distr.360 motor--our first time out in Martin mich car ran 10.4,10.5,10.6,10.4 and was going thru the traps at 7600,last run zach said something happened at the far side of the track that run he was 11.6 so a full sec was lost and only went thru the traps at 7,000 so car came back to Wis and went to test and tune the next tues car ran 11.6,11.7,11.8.11.5 going thru the traps at 7,000,so we still lost 600 rpm,last night we went and it was the same at 11.6,11.7,11.5 and only going thru the traps at 6700 so in total every time out were losing rpm's??? a total of 900 rpm's has been lost and now we are lost???????? car launches like a mother 60 ft times around the 1.5 consistent time,Where does a car drop a sec and 900 rpm??????? Converter???????? Thanks Steve