TD495T

what is the best way to tell if my convertor is goin bad? running this past sat. nite my reaction times were all over the place and car started slowing down first in mph then et's and the track got better as the nite went on, my car usually runs 4.80's & 90's @ 141mph but my last pass was 5.02 @ 135. have been racing for over 10 years but have never had a convertor go bad so don't know what to look for.

thanks,

wade