I have a 91 rs 5.0 and I set the timing to about 4 degrees advanced and it ran excellent the next day or so I noticed a loss of power so I reset the timing to about 3 degrees advance and it ran great until the next day. Any ideas or suggestions? Thanks for any insight.

 

Are you following these steps = https://www.thirdgen.org/settingtiming
I don't have a scanner so I have to do the last step under load and by ear.
I run mine at 4* advanced and it will jump off the line. Thats were you will feel it,off the line it will have a much nicer throttle response. Of course having a 3.42 ratio doesn't hurt either.

 

Maybe you have other problems, like tune up parts, low fuel pressure,ect.

 

may be a dumb question, but did you remember to retighten the distributor hold down bolt after setting the timing?

 

That's what I'm thinkin too .. It's gotta be tight ! When u rev the engine the cam will actually turn the distributor and change ur timing if its loose .. Sometimes it can even turn a * or 2 and settle back to where it was at idle