PMDG B747-400 & B747-8 Flight Model

Not sure if this belongs here or somewhere else, but I am experiencing the same problem with poor landing performance with the new PMDG B747-400 v3 and the B747-8 v3 aircraft as other pilots. As a result I replaced the B747-400_PW.AIR file with one from a previous package for B747-400X DVD that I had on hand. The file names are different so I modiied the name but the airplane doesn't seem to mind. It definitely lands better and I am satisfied this is good. Now I want to do the same thing with the B747-8i but I see the file size is different and am relunctant to do more.

I really like the -8 and the 8F but I can't figure out a better way to make decent landings. Changing the .air file on the -400 solved that problem but from there I am stuck. I have been flying sims for almost 40 years so I know a thing or two about how to do it but the -8 is kicking my tail.