Transmission ?

I have a 66' Lemans with a 455 in it. Recently I took her out for a drive, I went about 5 miles from home and on the way back, she really would not start going until I got her to 4th gear. 1st through 3rd the rpms would just rev and she would barely go any where. Was wondering what you think the problem is and if it is something that an average person could fix.

Thanks,
drum

Could be the clutch slipping. Hope you figure it out...sounds like a nice ride.