1998 Chevy Tahoe truck wont start

I have a 98 chevy tahoe with 108000 miles I have had this truck for about 4 months now and shortly after I got it it started having problems starting. The truck will try to start and then just shut off a couple of hours later you can go try it and it will start right up and run fine. After the first time it did it the speedometer stopped working. The problem has been off and on at first I thaught it was the fuel filter so I replaced it and that didnt help. So I tried some fuel system treatment and the truck was good for a week then started again. This time the check engine light came on and said the cam timing sensor was bad so I changed that and that didnt help. When I was looking under the truck I noticed some wires rubbing on the front driveshaft and a couple had beed eaten through so I sauldered those back together and shrink wrapped them and also replaced a blown fuse and the truck has been fine for a month now all the sudden it is doing it again. When it does it I can hear the fuel pump kick on and pressureize the system so I really dont think that is the problem. It sounds more like something is cutting off the ignition system.