My question is if a TCC solenoid or dirty valve.

My question is if a TCC solenoid or dirty valve body can cause a transmission to slip between first and second gear? The problem is intermitent, but sometimes it seems like it is in neutral when shifting between first and second. Sometimes the shift is fine. The rpms rev up but the gear engages once the rpms come down when the problem happens. The fluid is dirty. A tranny shop says the only problem could be the second gear clutch and wants a rebuild. The shop said that the solenoid only engages on the highway at high speeds, however I have found other info that says they are pulse modulated at much lower speeds. Normally I would have rebuilt, but a quick search online told me of the solenoid and valve body issues with this particular van. Rebuild or replace tcc solenoids and clean the valve body? Specifically, could a tcc solenoid or valve body issue cause the problem described, or is the cluch the only possible cause?