300E Trans again

Hello All

The tranny in my 87 300E has been shifting perfectly for 1000 miles since I installed the new kickdown solenoid, until yesterday. Now it is doing the same thing; not upshifting into final/4th gear again. Do you think I need to get the inner valve part for the kickdown solenoid(what is it called again)? The cable is adjusted and lubed, and I unhooked the kickdown switch with no difference.

Any Ideas? Maybe an additive or something?

Any problem with adding a second bottle of Lubegard or adding some Lucas Oil? I have one bottle of lubegard in it now.

Thanks again for the help and advice

Angel