DETONATION killed my motor 2 times now... distributor?

[mighty spx]

I had the motor rebuilt 3 months ago, put it in the truck and got it street legal 2 weeks ago. hit the interstate thinking it was all good and didnt get a mile before this happened
20131101_074200.jpg

pulled the motor and sent it back thinking it was mechanical failure, they warrantied it got it back put it back in the truck got it running good and took it down the road. then bam!! it happened again trying to maintain 55 mph round 2
20131102_144232.jpg20131102_142059.jpg
so needless to say, im not going to send it the machine shop for my screw up. so im stuck fixing it. no problem there.. but what im looking for is the root problem to this. i run 93 in the truck, with a new weber. set to factory timing specs.. Bad distributor? im at a loss