sclserviceCHAMBERS

Well I have a 2000 silverado with a 4.3 that has served my needs perfectly until now Keep in mind I am the product of the 60's and weaned on 283,s 327.s small blocks etc etc in fact I own a 66 vette so this computer stuff is really a learning curve and I'm 64 years old set in my ways
What is going on it when I start it when cold it idles perfectly revs up just fine but when I put it in drive the idle is rough go to drive it it hesitates until I feather the gas then it runs ok UNTIL the engine warms up then when I accelerate it sputters bogs down like it's starving for air or fuel then when you floor it it bogs down with no power. Being that it has VERY high mileage (400K) I decided to replace every sensor on the top end ( TPS, EGR, you name it, I cleaned the throttle body, did the seafoam thing injecting it into the vacuum to blast the crap out, replaced the cats, replaced the 02 sensors, the coil, new plugs, new wires, new MAF checked fuel pump new filters, compression, timing ( which you cant adjust) you name it but still zip It is starving for fuel or air I haven't checked the injectors yet but that is next ( they are only 2 years old) or the regulator etc for fuel leaks SO what do you think is going on?? I've gained a small education looking at those Utube fixerup videos but thats all I've gained So I need a direction to go to I'm not to savy on the names of these components so be kind as when I looked up how to check the air flow I had to look up what MAF stood for before I knew what the hell they were talking about but I am gaining an education and understand the "theory"
Thanks ahead of time ( I think)