Please help me decode this 68 roadrunner fender tag. Thank you !

Do a quick online search for Mopar VIN decode. You will get all you need.

Try here.
https://mymopar.com/vin-fender-tag-build-sheet-decoding/

Just noticed your SPD (scheduled production date) is 6/23. My 68 Coronet has a date of 6/26; 3 days after yours. What factory did yours come out of? Mine came out of the St. Louis assembly line. Looks like yours is out of another location.
looking at your sequence number.

1st row (bottom line)
RM21 = Road Runner 2dr coupe
62 = 383 4-bbl HP V-8 335hp
3 = 4 speed transmission (floor shift)
44 = F70x14 Redline steel belted tires
A06 = Scheduled Production Date - Oct 6, 1967
172182 = Sales Order Number

Next line up
5 under the 2 = drip rail moldings
4 under the A = 3:23 rear axle ratio (8.75 housing)
8 under the X = Sure Grip

D under the T = Deluxe Interior
4 under the R = Vinyl split bench seat
S under the M = Silver and Black

P under the P = Roof Color - Matador Red
P under the N = Body Color - Matador Red
1 under the T = monotone (not two tone)

B under the U = Upper door frame color - Black
B under the S = Black horizontal stripe (pinstripe)

Next line up
4 under the C = H.D. Suspension & front sway bar
1 under the R = Radio - Music Master (economy 2 watt)
7 under the T = Tachometer
2 under the X = Tinted windshield only
6 under the Y = Black Vinyl Top

Next line up
6 under the m = driver side outside remote mirror
1 under the u = Sold car (ordered)




Nice car - notice my avatar

Still cracks me up that Plymouth called the base interior (shared with Belvedere coupe) "Deluxe".

Cool car, would be gorgeous restored.

Red, Ti-toc-tack AND a 4 speed car!?!?! awesome. My car didn't come with a fender tag. Always bums me out.

Red with a black top would be a nice looking car.

the non-rallye dash b-bodies from 1968-'70 had the "postage stamp" tachometer without a clock

Yep
Missed it.
corrected it
thanks