LT1 swap...tricky speedo... swap went great but now speedo flickering

[GonzoLT1silverado]

iv got a tricky one here for yall.. I just replaced my TBI 350 with a 96 trans am LT1.. The swap turned out great everything so far has worked out perfect but recently my speedo has been acting up , il be driving along and my speedo will drop to 0 for a sec motor and trans fteaks out and then itl go back to normal agian it dosnt do it to often. i know that the PCM runs motor alot off vss signual to shift and to adjust engine.. Wen i wired everything up rather than bypassing the trucks vss bfer i wired the PCMs high and low range vss signal wires to the exsisting vss wires on the truck (piggy backed them off the orginal vss wires) thus the trucks vssbuffer still got its high and low ranges to run speedo and my pcm had high and low ranges to run everything else and i spiced everything properly sodered and waterprof heat shringed ect ect so i dont think its the loose wire case (not rolling it out but also not convenced its that) could it be that my Vss is givn up and i need to replace it, or was it wrong to piggy back these wires iv ben driving it for a week now and this just started.. the speedo and pcm seem to fault at the same time and there only connected thro the VSS in t-case.. if the vss buffer was faulty the speedo would flicker but motor would run fine ..right? lol i told yall it was tricky any info or thoughs id apresate it thank y'all