What an experience, eh?
First of all, did 3rd work before you took it in to the shop? If it did, then they probably either:
1 - used the old valve body gasket or ripped the new one putting it in,
2 - torqued the Valve Body wrong or not at all,
3 - put wrong parts in or replaced parts that you had intentionally left out,
4 - the possibilities are endless.
Hey, I won't even let a tire shop put my car on the rack, I carry in the rims!
I have had so many bad things happen in the hands of others that I have no trust left for them at all - broken windshields, stripped lug nuts, bent chassis, etc. And they always deny that they had anything to do with it... It was like that! Yea...
Anyway, if the clutchs are slipping, I wouldn't drive it unless you are ready to overhaul it - but it may just be time for it. The stock tranny's don't last very long.
And a slipping clutch pack lasts even less...