1966 C10 Exhaust Resnonance issues

[njc1230]

Hi guys, hoping ya'll mind might have some answers to this conundrum. My 1966 C10(short wheelbase) has a 350 Chevy(w/headers) and 700r4 swap and I just took it out for a test drive after finishing a 2.25" exhaust system. Above 1800 rpm, or so, the exhaust is tolerable, but when it drops below 1800 rpm it develops an unbearable resonance. Could barely talk to my dad in the seat next too me, and it quite literally started to give the both of us a headache. I'm using 2 chamber mufflers included with a Speedway Motors kit I ordered a few months ago and I'm less than confident that the mufflers are quality. When I got the truck it had this horrendous 2" exhaust system with glass packs that made it loud, but had no resonance. However, I've seen people put in more restrictive mufflers and have no resonance issues either. Do I need to go back to glasspacks or a less restrictive muffler, or can I go to a quieter muffler?

The kit:
https://www.speedwaymotors.com/DIY-U...-4,284231.html