KW T2000 smoke/bad fuel economy

So I'm hitting a wall with this truck, kw t2000 cummins isx cm871. A while back turbo went to #### for the second time vgt inside was stuck replaced truck was good then egr went to #### replaced as well that's when all problems started nnow truck is good for a couple of days then out of nowhere starts smoking like all hell and full goes to #### threw another egr code so of course it'sunder warranty and Ii replaced it again when taking off the egr plug found that two of the terminals on the plug were burned out replaced terminals and egr still getting same issue it went from fuel being at 7.5 mpg to now at 4.8mpg everything points to egr again but Iit doesn't make sense two bad egr in a row. So my question is j know there is a lot of cummins experts out there can u guys jump in on this and give some ideas because I'm hitting a wall can think of anything else the most current code that pops up is mid 128sid 124. Any help would be greatly appreciated