Export plays choppy. What did I do wrong?

Question

*I'm new to PremierePro and I don't know much about video editing, I've learned only what I need to know to do the projects I've done.  Previously, I used iMovie11*
I exported my project, and opened it in Quickbooks 7 to view it before I uploaded it to YouTube.  It plays very choppy and I don't know what I did wrong.  Here are some details:
Mac OSX 10.9.1
Premiere Pro CS6 Creative Cloud
My project is a 3-minute sports highlight video.  It needs to be posted up on YouTube by TODAY.  I've been working on the video for 30+ hours, and on the export process for 5+hours.
The clips I used are from various sources: Nikon D3200, GoPro, and professional video (hired a guy), and some are clips from a previously created highlight film that the client's school sent me to use (.mov and .mp4).  I did not know anything about frame rates before today. In my troubleshooting, I've learned a little, and I checked the frame rates of the clips in my project.  Some are 23.97, some are 29.97, and the GoPro clips are 59.97.  The clips are meticulously timed to a music track and spoken interview with music in background.  Some of the clips from the videos the school sent me are in slow motion (which I've timed the music to), but my original clips are all at normal speed.  The clips from the GoPro seem to be sped up (which I've timed perfectly to the spoken interview) but I didn't do anything to change their speed (59.97fps).  The video is just over 3 minutes long.  The playback in Premiere (in the upper right window) is perfect. 
My goal is to have a nice quality video on YouTube.  It's critical. 
I have tried exporting a couple of different ways, and have the same choppiness.  I'm nearing the end of another go-round export, and will soon know if that made a difference but I doubt it.
Before I exported, I "rendered" the project and the audio.
My export settings are:
H.264
preset:  I've tried YouTube 29.-- 1080 (whatever that preset is exactly?) and Custom setting (where I changed the target bitrate and the max bitrate)
Video:
aspect- square pixes
NTSC
Profile- Main
Level- 5.1
Checked "render at Max depth"
Bitrate Settings:
VBR.2 pass
Target bitrate: I tried it at 45, and currently experimenting with 50
Max Bitrate:  300
Key Frame Distance: 90
Checked "Use maximum render quality"
Summary: 1920x1080(1.0), 29.97fps, Progressive VBR, 2 pass, Target 85Mbps, Max 300Mbps, AAC, 160kbps, 48kHz, Mono
Source Sequence: 1920x1080 (1.0), 29.97 fps, Progressive, 0:03:24:03, 44100Hz, Stereo
Each time I've exported and experimented with different settings, it takes about 40 minutes.  I could do this all day, but I'm wondering if my problem lies in the variable frame rates of the clips within the project.  I really hope not.  As I said, everything is meticulously timed to the audio..  The playback in Premiere is perfect, not choppy. 
Repeat:  I'm a beginner.  I grew out of iMovie and I'm now learning as I go on Premiere Pro.  Please understand that I don't know what most of these terms even mean (frame rate, bitrate, encoding, key frame....). 
PS. recent export complete.  still choppy regardless of the changes I made (I checked "match source" and changed target bitrate from 45 to 300)

Answer 1

>opened it in Quickbooks 7
Huh??? You opened a video file in a checking program?
>wondering if my problem lies in the variable frame rates of the clips within the project
No version of Premiere, Pro or Elements, will PROPERLY edit a variable frame rate video
Adobe/Jive have a BAD title for the SEARCH THIS FORUM function
Go to http://forums.adobe.com/community/premiere and, in the area just under Ask a Question, type in
variable frame rate
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