So the problem really started late last year and has gotten worse this year.
It has drove me nuts because that was when i went from a 3000 stall converter to a 4200 stall.
What i finally....think i have figured out is the load between the two converter. The 3000 converter was a Stock Converter that was tweak to get 2800 out of my 340 and stall around 3000 with my 408.
The new 4200 converters stalls much higher for sure, But is TIGHT. in other words my 3000 converter took vary little throttle pedal to stall at 2200(rpm that i leave the line at) how ever to stall the new 4200 converter to 2200, it take more throttle/More Load to get to that same 2200 rpm launch speed. Now this year i started out with a 2 inch taller tire that added to the problem.
I may be wrong but that make sense in my mind. I just didn't get it when i first started fighting this problem.