Appreciate the reply.
One would think that once transcoded to MP4 we could rule-out that it's the format's fault. Nonetheless, the clip was shot on a little Toshiba Camileo H-30 in 720p (30) -- I just double-checked that, so it wasn't 1080p at all. My apologies for that mistake.
Last night I went and tried working with the clip and I _can_ edit it in PD, but it apparently renders it for preview on the fly and it makes things really slow-going. (But then whatever's been rendered has a green-bar in the "timeline" area of the screen, and that can be re-played no problem.)
The workaround is almost to import the clip, add it to the timeline and make it play the entire clip (slowly, studdering through it all, maybe overnight) and then come back and use it, because PD has rendered it.
I have "MediaInfo" Installed, so I'll give you what it spits back about the clip:
Format: AVI
File Size: 191MiB
Duration: 6m 18s
Overall bit rate: 4 239 Kbps
VIDEO STREAM
Format: AVC
Format profile: Main@L4.0
Format settings, CABAC: Yes
ReFrames: 4 frames
CodecID: H264
Duration: 6m 18s
Bit rate mode: Constant
Bit rate: 4 001 Kbps
Width: 1280 pixels
Height: 720 pixels
Display aspect ratio: 16:9
Color space: YUV
Chroma subsampling: 4:2:0
Bit depth: 8 bits
Scan type: Progressive
Bits/(Pixel*Frame) : 0.145
Stream size: 185MiB
Thanks again for the reply.
-AJ