Airball you live in Washington State as myself, that means your old girl is smog exempt. So you may do whatever you like to your trucks engine to fix or upgrade parts. Perhaps a Weber carb, a header, cold intake, there is an endless supply of fun aftermarket items to enhance your already fun truck. Sometimes the ole Mikuni carb (POS) just isn't going to give it up any longer. Investing in a new carb will bring a new life and more horsepower to that girl in a great way. Easy to install and set it and forget it also. Welcome to the zoo

As for your egr valve and sub valve. Right when you think you cleaned it, you may take another looksy. Those darn things collect carbon crap from the carb through the intake manifold, all the way to the #4 exhaust port of the head. Sometimes the only way to clean them is with a rigid coat hanger and get ready for a pile of carbon chunks to fall out. As old as your truck is, like mine..you may also look at old catalyst converter. I think your truck has 2 of them if not mistaken. It maybe time to pull the exhaust pipe out and start jamming a screw driver into cat to gut that exhaust restrictor completely. That stuff inside is a silver mine also, dispose of the stuff in a green way if you can.

Cold weather in Washington causes my truck to start a little harder also.