Gas water heater pr valave leaking

Hello All, Just replaced all the water lines from the street to the house and all the baths and kitchen and laundry room. The psi at at the faucet outside reads 56 psi and the water supply at the clothes washer reads 56psi.
My Hot water tanks keeps popping off so I checked the psi at the water drain valve on the tank and it read 78psi, didn't drain any water off and let it build psi back up, i just screwed it on and checked the psi. I do not have a
psi regulator on the main line coming in cause the psi was only 56 which I understand is ok, I was going to replace the valve but thought I may have a issue the psi reading 78psi on the tank. What do you all think.
Thanks

Some water meters have a check valve built in, which would necessitate an expansion tank, but since you didn't have this problem before, unless the meter was changed with the new plumbing, that shouldn't be a factor. That would lead me to believe the TP valve is shot. Simple and cheap to fix, part is available at any hardware store. I think the slight rise is pressure at the tank is normal since the heated water expands and will cause the pressure to rise, but the real excess is absorbed back into the city water supply. 78 psi is not enough to pop a properly functioning TP valve anyway. Try a new TP and holler if that doesn't fix the problem.