The Tremec and the T5 are totally different transmissions.  The "Z-Spec" you hear everyone talking about is the version of the T5 currently sold through Ford Racing Performance Parts, and is basically a standard World Class T5 with a close ratio gear set and all the synchro updates.  It's a good trans designed for moderate power with a rear gear in the 3.50 or higher range.

Tremec 5 speeds were designed as upgrades to the T5, which had a bad reputation for durability.  That reputation is somewhat undeserved, but if you abuse the trans in a heavy car they do tend to break.  Tremec was at that time a separate company, as the T5 was built by Borg/Warner.  Eventually Tremec bought the T5 rights from Borg/Warner, adding to confusion about Tremec 5 speeds.  But, I digress, Tremec started out with the 3550, and eventually they released an even stronger version dubbed the TKO.  Today, those boxes are still out there used, but the current iteration of the Tremec 5 speed is either the TK500 or TK600, with the number being the torque rating of the trans in lbs/ft.  They are tough, well built transmissions.  However, there have been complaints about the synchronizers and shift quality since the first Tremec came off the line.  The issue I feel is that the Tremec has never been factory offered in any vehicle, and thus has never had to conform to OEM tolerance for smoothness, NVH, etc.  The shifting is almost alwasy described as "notchy".

I will say that over time they tend to loosen up.  If your buddy's trans is new I'd drive it until it loosens up.  If its used a rebuild might be in order.  Missing a powershift tends to damage the engagement teeth on the gear, rounding them over and mushrooming them, making shifting even harder.  Sometimes the trans will jump out of gear if the issue is bad enough.  The synchro rings oddly enough tend not to be damaged, and I've pulled good rings off fragged gears many times. 

For all things Tremec I'd advise speaking to the leading man in the field: Bob Hanlon from Hanlon Motorsports.  I've known Bob for years.  He's a great and knowledgeable guy.  Here's a link to his wensite:

http://www.hanlonmotorsports.com/

I have raced with a Tremec for many years. And you are right, it is a chore to shift correctly. For one it is a big transmission. Center shaft distance is big for a 4 or 5 speed. Good part of that is that it will take a beating. Bad part is the parts are big and heavy. So it shifts like a truck. I have found that you need to match revs very closely to get any kind of fast shift. The higher the revs, the worse the problem. I have found that an unusually high idle setting helps a bit since that will cause the engine revs to slow less quickly. I left the choke linkage in my car but removed the choke plate so I can use the high idle cam to get to that unusually high idle. Best thing is to learn to keep some throttle during shifts to keep the revs closer to the synchro point.

The other thing you might want to check is bellhousing bore runnout to see whether or not the input shaft and crank centerlines are inline.  With factory stuff this is rarely an issue, but since the Tremec was never a factory trans and requires a different bellhousing or adapter there is some potential for misalignment. 

Then I call BS.  The T5Z has the best synchro setup ever offered in the T5.  If its not shifting right something is wrong.  How's the clutch release?  Fox body cars always did best with some form of clutch adjustment other than the cable end at the fork.  I used to run firewall adjusters.  It made setting pedal height a breeze. 

Wow, didn't know SB made clutches for cars, cool.  They get rave reviews from all the Diesel guys who run manual trannys.  Amazing holding power in trucks making north of 1,000lbs/ft. 

Yes, it should be ATF.   

All good advice, I will pass it on to my friend and his mechanic because he wants to do what's right.