Slant 6 turbo how to set timing please help I will even pay

Here is what it has a 4 barrel Holley 390 cfm a t3 t 4 turbo it's a love hate relationship with this car some times it would run like a champ and other day I be driving it and it would start back firing and hesitate not good when the turbo is boosting the four barrel didnt have a place where to put the vacuum advance hose from the distributor so I wouldn't use it and set the timing at 15 # like I said it would run good and the next like shxxxxxt. It's driving me crazy so I installed a new distributor and can't get it to time right should I get a msd 6 btm will this solve my problem our is it some thing else it feels like the moon light has to hit it just right and she runs like a rape ape I'm only running 5 psi o yea if I set the timing at 15 # and and use manifold vacuum to the distributor it send the timing to the roof Please help I really want to finish this car take it the track and see want and old slant 6 can do