1992 Chevrolet Cheyenne Running issues

I have a 93 chevy truck I replaced both head gaskets on it and befor it ran good but the gaskets were bad so I devoted to replace them when I got it back together it ran sluggish and I checked my plugs and replaced them and checked valcums and replaced those so I looked at the timing again and when I time it at.0 it moved passed advanced on the timing mark witch is top dead center and it runs goo for awhile ten like I get down the highway it dies and I'll have to wait and start it and I'll get the same distance and it dies again so I timed it agin and it keeps doing the same thing the timing mark goes strait top center and te truck cuts out and dies so I don't know what it would be I checked and working on it for a month so I thought I would ask on here and see what u guys say anything helps!