I have a 2000 f350 with a 7.3 and a zf6 I have a ts 6 pos chip on it when I first put the chip on the truck would black smoke like crazy and over time it has gotten to were it smokes less thepower Iis still there but it just smokes less what causes this? I have a buddy who has had the same thins happen on three 7.3s he has had

 

how old are the tunes? they should not smoke like crazy all that is doing is hurting you $.
how many miles on the truck, how many miles has the tuner been on it?
have you check for codes?