95 K1500 EGR Causing Stumble

[DRS 95 Silverado]

Have a 95 K1500 TBI 5.7 auto trans. Only has about 67000 miles on it. When I start up my steep driveway it likes to stumble, fall on its face. Got to checking and it seems to be the EGR valve causing it. As soon as it gets warmed up some it goes into operation like its supposed to so temp sensor and solenoid are working right. I replaced EGR valve about 8 years ago with the newer part number GM valve. If I unplug it it doesn't stumble. I checked solenoid output with gauge. It's getting vacuum at very little throttle but I thing its supposed to. I know its works with the  vacuum and exhaust pressure together. Read that sometimes they just get weak and open too easy. Also read that if you don't have enough exhaust back pressure it can cause it not to work right. I had exhaust system from behind converter back replaced about a year ago and thats when it seems to get worse. Its just a single exhaust but the muffler he put on it has a little rumble to it like a high flow one if that makes any sense. Are the EGR valves on these old TBI trucks that touchy. Thought about just replacing the EGR valve but I hate just throwing parts at something. Any opinions or answers would be appreciated.