should be 3.8 v6

Actually the 1999 Lumina used a 3.1L engine good for about 150HP, give or take.  This is a 6-cylinder fuel-injected engine.

it can be either a v6 3.1 or 3.8  seen both on it

I've also seen a 3.4, but that is a somewhat rare option...

If it is the Ls, which you did state that it is, then you have th 3.1(31000) V6 with a 160hp. The only way you would have the 3.8 is if it was a LTZ trim.

i used to have 97 with the 3100sfi engine v6-160hp.
the car was over heated my mechanic said that the crank was broken so i replaced it with the new v6 3100sfi  with 175hp.
i would rather had the 3.4 twin cam or the 3800 series with 215hp.