can some help with turbo 350 trans issues?

Hey Rodders, here it is- I recently installed a 350 chevy motor and trans that was in my 1958 truck into new project truck,1966. Both have been in the 58 and running great for last two years!(truck has a nice cam)I have been in formed that the trans modulator should be hooked up to rear intake manifold vacum.(it was always on the vacum advance line with distributor to top carb vacum)and it ran good! So I moved this connection for modulator to the rear vacum line via" a tee in the brake booster line. The darn motor always stalls out when i put into gear. I have tried to put back the way it ran before ,but it also stalls out NOW!!! Don't know why..It used to run fine prior to swap.:( going crazy .......can someone help??

Check for vacuum leaks since you were fiddling with vacuum lines.

Hey thanks to the help offered.I was able to locate the root of my problem.It was rubber vacuum cap on the carb that had tore apart. lets say causing a serious vacuum leak! problem solved and runing really great.:D