I have 2001 Chevy Tahoe with 4L60E tranny. The car has only about 160k miles as for now. Last year I installed TransGo Shift-Kit 4L60E-HD2 - actually only the parts that make the shifts firmer and quicker, no shims for the hard-shifts, no clutch springs. The valve body looked in good shape, only the separator plate was showing a slight wear on check-ball areas but nothing serious. The truck went perfect after.
However during last week I noticed that when the transmission is warmed up after longer drive, there's very short RPM increase during 2-3 upshift. It's about tenths of RPM. The shift speed seems the same like it was in the past. This usually happens when applying a moderate throttle for acceleration. Could it be valve-body problem?
EDIT: The fluid still looks and smell brand new.