Updating media

I am currently in the process of converting my collection of HI8 tapes to DVD. However, on some of the tapes the capture program is dropping frames, resulting in 1-5 seconds of very choppy footage. Sometimes this results from opening other more intensive programs during the capture, but for others nothing is running except the capture program. The cpu is only at 5% and RAM use is only about 25%. I have cleaned the head in the player and am still having the problems on several tapes. The problematic tapes are mostly 5-8 years old, so that may be a factor, though they have been stored in a dark temperate controlled room. Is the frame dropping a result of degradation/dirt on the tapes or from the capture program? If it is a result of the tape, is there an inexpensive way to fix it, or will I just have to live with the slight blip? If a computing error, would a dedicated capture card or different software fix the problem?

Camcorder: Sony DCR-TRV103 (about 8 years old)
Program: PowerDirector capturing to .avi then letting Nero fitting it to DVD

Thanks