Are you sure the blades were the problem and not the pitch or the RPM you were running? New blades come with a sharp edge and full height, so they grab way harder than a worn set that's already broken in and riding flat. On a second pass especially, if the machine is set too flat or you're floating too early, fresh blades will chatter and dig no matter what you paid for them. Price doesn't change the fact that new steel needs a few passes to seat and dull down before it lays smooth. Did you check the blade arm bolts and the spider plate for slop before you swapped sets?

Ever had one of those where you go back later and realize the whole problem was staring you in the face the first five minutes? I bet half the "weird" calls techs get are just some previous guy's lazy fix, a zip tie, a bent bracket, a screw run through a wire.