The shifting quality is a roll of the dice. If the trans has the correct lubricant and break in, It should shift fine. If it does not, then it may not shift as smoothly as the T5. If you are going to replace the 3rd gear syncro, you should be prepared to refresh all of them. Tremec 3550/TKO 500/600 parts are much more expensive than T5 parts.
I don't know how you feel about the DYI thing when it comes to gears, some people don't like the idea of working on transmissions. If the DYI transmission fix idea isn't something that you would rather leave to someone else, here are some resources:
See
http://www.ttcautomotive.com/English/onlineorder/product.asp to download a FREE service manual for T5 or Tremec 3550/TKO
You will need the Adobe Acrobat viewer which is also a free download –
http://www.adobe.com/products/acrobat/readstep2.html
See
http://www.hanlonmotorsports.com/ or
http://www.ddperformance.com for parts
http://www.hanlonmotorsports.com/ also has a video on how to rebuild your T5 or Tremec. It costs about $20, and is worth every penny of it.
I did a Tremec 3550 rebuild, and it wasn't that difficult. The video was an immense help, and I would recommend viewing it. At $20, it will give you an opportunity to look and decide for yourself if you think that it is something you want to try to do.
For Tremec 3550 and TKO's:
You will also need a magnetic base and dial indicator to measure the endplay ($40-$120).
http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=1354&PMCTLG=00
The tricky part is that you will need some shims to adjust the endplay in the two shafts: the new bearings will change the clearance. There is no way of telling what it will be until you get to the point that it is time to measure and check the clearances. Halon has the individual shims if you can wait for them. If you can't afford the wait, the auto parts store can sell you some shim stock and you can make your own, or have a machine shop make them for you. The shim stock comes in brass (easy to cut) and steel, in varying thicknesses.
That's where the dial indicator & base come in - there is no way to get the clearance right without it.
Shims for T5 – peel & place
http://www.5speeds.com/t5/shims.html
The new system only requires 3 shims. The main drive shim is .067” thick with peelable layers that are .002” thick. The countergear shim set uses a solid .087” service shim and a .077” thick peelable shim that has .002” thick layers.
A razor is required to start a “peel”. Use extreme caution. You can actually just peel down a shim until the desired preload is achieved. Remember to always seat bearing races by hitting all input, output, and countershafts with a rubber mallet before your final measurement.
Getting the car jacked up high enough to get the trans jack in and out from under the car was somewhat challenging. If you use a transmission jack, you will need 24" of clearance between the bottom of the car and ground. That means you will need a SUV jack and very tall jackstands. Since I didn't have a helper, getting the trans out of the car and back it was one of the more difficult things about the job. I built a trans jack out of 2x6's, some angle iron and a $25 floor jack. If I hadn't done that, I would have needed a helper or to rent a commercial trans jack. At 100+ pounds the Tremec 3550 was far too heavy for me to lift by myself.