bad backfire after complete new timing set installed by a shop.

[EGAZ]

I had my entire timing set installed by a recommended shop. Directly after the installation my car has a bad backfire under hard acceleration. The shop reports they did the timing correctly, but now have no idea as to why my car is backfiring. I never have had this issue before and am curious to know if the shop just installed the timing set incorrectly by just one tooth.
My car isn't throwing any codes. I run three sets of tunes, which all work well.
Any thoughts about this issue?

 

[Dino Dino Bambino]

The backfire is almost certainly due to incorrect cam timing (one or two teeth). Unfortunately you'll need to remove the timing cover again to correct it, and new phaser bolts.

 

[86GT351]

The backfire is almost certainly due to incorrect cam timing (one or two teeth). Unfortunately you'll need to remove the timing cover again to correct it, and new phaser bolts.

This

 

[DieHarder]

I'd take it back and tell them to verify/fix it as I'm sure it wasn't cheap. Hopefully, it's not making noise and no bent valves.