New to the forums, got a '00 SL1 with 157k on it.

Around 153k thought i felt the Clutch slipping. New clutch and front input shaft seal replaced. Shortly after that a shift cable broke/frayed right at the tranny, I replaced that as well. And it still feels like it slipping/chatter.

Took it to a shop today, told me its running like crap missing left and right. CEL was blinking, code registered as a near stall/major misfire or something along those lines.

No to bad at working on my own car, but I am no mechanic. I replaced my plugs about 5k miles ago right around the time this all started. If I were to do a tune up to get it running smooth again and stop the misses, etc. What would that entail, keeping cost in mind.

 

Define tune up! Back in the day it was to replace worn out parts and adjust what was replaced or required adjustment.
Usually, plugs, points, Air cleaner and adjust carburetor.
Today, with materials being what they are and computor controls being what they are.
There is nothing to adjust.
What is adjusted is done by the computor everytime the engine starts.
Plugs can last up to 100,000 miles depending on the material
leaving just the air filter as needing to be checked and replaced.
If needed.
Spark plug wires are a possibility unless coil modules are attached to spark plugs. (I'd have to look. Don't remember. Wires could be bad, coil modules or modul could be giving problems. Mayby a vacuum line screwed up. Something is not right and that needs to be found.
And at the moment, if the mechanic you are using is the best in the area, I'd look for a second opinion. One that actually tells you something useful.
Get any error codes off of a computer read out. Are fuel pressures right?
Dunno, but what scares me is the word Tune Up. Nothin there to tune, and dang few things to replace.

 

I concur totally. If your "mechanic" won't tell you the actual codes, go by an AutoZone store (or similar) and have them run the codes. Post the actual numbers here, and we'll try to help .........