Have you tried one of the ozone generators? The larger ones seem to get rid of owners according to some individuals who have posted here. Paneling? If paneling, either wood or aluminum, was replaced and glue was used then maybe it is outgassing which is causing the odor. Was the wood flooring coated with something when it was replaced?
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system