timing issues

I decided to start looking at some of reasons I had such a slow day at the track and Timing was first. I had been running about 6-10 BTD and moved it to 15 just to see how it responded. Well I put the light on it and it climbs to 35 and right about 3500-4000 rpm the timing jumps beyond my mopar timing tape. It goes to 60 i believe. It is very quick it does not ramp to that position it jumps like someone flipped a switch. I tried adjusting the reluctor gap with no change. Any ideas? I want to think it's the distributor but not sure how it could jump like that.