Since early april when Sp 4.0 came out we've been having troubles opening large assembly drawing. A 10 meg 5 page drawing that took 20sec to open with sp 3.4 now takes about 10 mins in sp 4.0 and sp 4.1. Since I had to stay with at least Sp4.0 to be able to upgrade my Cosmos to sp 4.0. I had to open the assembly model first fully resolve than open the drawing. 99% of our assembly drawings have an excel based BOM. Yesterday I deleted the excel BOM in a large assembly drawing, and inserted a BOM table. The drawing opens fine now. There seems to be some conflict going on in the back ground with sw and excel since sp 4.0.