i recently got a 60 series muffler finally installed and my dad says i will burn my exhaust valves eventuaklly cause back pressure was reduced by 5% and my ECU/ chip that regulates your engines performance, isnt programmed to handle the muffler. now i trust my dad, cause hes been around the block a few times and worked with cars alot longer than i have, i just wanna prevent this from happening if it even happens, any suggesttions?

Im sorry to tell you this, and im not sure what certs your pops has... but i have never heard of that, i wouldnt worry about it.
If you were runing an open head then maybe, but dont worry about it.
i myself am verry mechanicly inclined, and MY dad (lol) has been a mechanic for all his life.. is a licenced vehicle inspector and has built/rebuilt more motors then their are hairs on my head... and other places.... and i ran my 80 Grand am with a 400v8 without exhaust mannifolds for a while and he wasnt worryed about it...he told me too...
On his 79 burb he has an open exhaust with a coupple glass packs on a 350 that he rebuilt....
You dont need to worry about your valves.
IF you just replaced the muff then you wont see the motor riching out.. and their is no chance of that...
Basicly Tell your pops to prove it.. to you and to us cus i would like to know how the heck he came to that conclusion