So after some light reading and contacting some transmission mechanics of mine I found there are really not much difference between the two electrically the 99should work just fine. So I checked all my connections and cleaned them thoroughly. Replaced the transmission ecm fuse and checked and rechecked everything. Then took it for a test drive. So to all the nae Sayers guess what go right ahead and throw yourself a 4l80 out of a 99 2500 series in because it works just fine. I had to adjust the shifter linkage a little to go all the way into park. And I went ahead and installed a manual tcc lockup switch while I was at it. This truck shifts smooth as can be and runs amazing.