Violent Bucking

Hello all, I've got a problem that has me basically wishing something would fall off of my car so that I would know what it is.
The issue I'm having is when I'm driving at any speed and I throw it in 5th and apply the gas the engine feels like it is literally going to jump out of my engine bay. At first I thought it might be because I was lugging the engine, however it will do this if I'm going 50mph or 90mph.
Something that might be a clue is, somewhere I have a random clacking that sounds like its coming from around the transmission, both when the clutch is engaged and disenaged, it sounds kind of like if you were to take a couple short pieces of metal and tap them together. However some times it makes the noise and sometimes it doesn't and whether the car is making the noise or not it drives the same.
1st > 4th gears pull hard and I can cruse fine in those gears no bucking/jerking/shuttering when the gas is applied.

I've replaced a few of the important sensors that come up when searching for this issue:
TPS, IAC, EGR, both oxygen sensors.
I've replaced the sparkplugs/wires, tested the timing from 8 > ~12 I run 87 octane so I don't want to chance any higher.
All codes come back clean.

This issue really puzzles me as aside from the 5th gear bucking and the noise I hear sometimes, the car runs really good and accelerates hard.

Thanks for any help.

Boosted92LX said:

Does it make racket in reverse? 5th gear and reverse use the same bearings I believe. I know they are together outside the main case if i recall.. might be a bad bearing in the trans. Or worse, a broken gear..

If it does it only in 5th at any speed it sounds like it almost has to be transmission.

Things that popped into my head were motor mounts, trans mount, clutch disc coming apart... but only in 5th gear?? Eehhh, sounds like it has to be trans.

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From what I recall reverse doesn't do the same thing as 5th.

Mustang5L5 said:

5th and reverse are separate inside the T5. Reverse uses an idler gear that engages the 1-2 slider and countergear inside the case. 5th gear is outside the case in the tailshaft.

I wonder if the 5th drive/driven gears have sustained some sort of damage or missing a tooth or two? Is the bucking directly related to the noise? Feel/hear at the same time?

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For all I know the transmission could have sustained some sort of damage, for a while the engine would get stuck on some RPMs and wouldn't drop back down to normal which I eventually fixed by cleaning out the engine and replacing the sensors I mentioned.
When I try 5th the only noise I hear/feel is what I can best describe as my engine trying to jump out of the engine bay.
The knocking noise if its going to do it, is more heard at idle and sometimes when I rev the engine, which is confusing because if I'm not mistaken a knocking from the engine, for say a bad bearing or a rod knock would be constant whereas this knock is random in rhythm and whether or not its going to do it at all.

So since it really seems like its the transmission that is the problem, is it safe to drive the car if the other gears are fine. Or will having 5th gear broken (and possibly many other problems with the transmission due to 5th gear breaking somehow) cause problems with the engine if I continue to drive it until I can fix it/replace the transmission.

Thanks for the help.