94 3.9 manual shift occasional backfires???

I have a 94 dakota with the 3.9 6 in it. I have changed plus wires cap, had the convertor replaced and muffler. i am getting 2 codes 21 and 32. I have done everything i can think of to fix this backfire problem. It does not do it all the time, but when it does it seems to lose power some. yoou can kill the truck goin down the road and let it start again and it pops out the tail pipe and runs better for a while. Any help would be appreciated.

I have a 94 dakota with the 3.9 6 in it. I have changed plus wires cap, had the convertor replaced and muffler. i am getting 2 codes 21 and 32. I have done everything i can think of to fix this backfire problem. It does not do it all the time, but when it does it seems to lose power some. yoou can kill the truck goin down the road and let it start again and it pops out the tail pipe and runs better for a while. Any help would be appreciated.
i dont know what 21 is but 32 is the egr mine does the same thing and im putting a new egr on it to see if that will fix it