Shift linkage problem ? 1974 911

[roadhugger]

Ok, here's the deal. I took my 911 in for a few repairs. One of them included replacement of the pivot bushing, shift coupler and shift linkage adjustment. I got the car back and was driving in traffic and she popped out of third gear. This happened four times in the same gear.

I took her back and my mechanic told me that some bolts were lose underneath the plate , so he tigtened them. Well, I still have the same problem. She worked fine until he made the first adjustment. Now, he's telling me it's the transmission. I refuse to believe this though. I think he's trying to screw me over. Why would it only pop out of third and start happening so suddenly?

any suggestions would be greatly appreciated.