97 Blazer Log Error P1406,P0420

I have spent alot of money in the last 6 months on this vehicle. The fuel pump went out, right after the ignition switch broke and coil wire burnt through.Had the intake manifold gasket, water pump, right rear axle boot replaced.Becuse of list of items dealer suggested, but I had a different mechanic do it. It now won't get up to highway speeds.I took it back to the mechanic who had it for a week, and it ran fine for a couple days, then back to slow again. I have reset the error codes.These errors are what I have now after replacing sensor 3 on bank 1, I had that error before.The codes immediately follow each other.It's fine in the city driving,35-45 mph no load, but it really strains to get to highway speeds,, sometimes almost bucks, have to back off, accelerator at times. I put an expensive injector cleaner in the tank, no difference, replaced the plugs. Oh, I have 120,000 miles on it. I bought it with 102, 000. 3 yrs. ago.Do I replace the fuel filter, (weird connector on one end?) Clean EGR? Is that located right on the front?HELP!!!! I'm getting the codes from a plug-in chip a friend loaned me, and we use his computer to read the logs.I'm trying to include everything you might ask.....Thanks in advance .....

Replace your EGR valve.

those codes are from a disconnected EGR valve electrical connector or a faulty EGR valve.

Remove the valve and spray throttle body cleaner through it and make sure the pintle is seating properly and all the carbon chunks are remove and reinstall with a new EGR gasket. Then reset the computer.

If that doesn't work, swap it out for a new one and you will be good.

Replace your EGR valve.

those codes are from a disconnected EGR valve electrical connector or a faulty EGR valve.

Remove the valve and spray throttle body cleaner through it and make sure the pintle is seating properly and all the carbon chunks are remove and reinstall with a new EGR gasket. Then reset the computer.

If that doesn't work, swap it out for a new one and you will be good.
Whie i had it out and I'm cleaning it, .I only got about a gram of carbon dust out of it,with a minature screwdriver, no chunks, and the pintle moves just fine.Looks like the gasket might have some issue, maybe a little stuck to it, got it all scraped off. soaking right now.....Well It didn't help, so I bought a new one and replaced it. Left battery disconnected. Made no change. I went to the auto parts store and bought a fuel filter, and replaced it, it was really clogged. But it seems to be worse right now. I forgot to reset the battery again. I pulled the chip, and the s.e.s. light came back on. Disconnected battery at 4:30 Ohio time ,will reconnect in a little while and see if codes are reset and if there is any change....I will get back to you...Dennis