What is my actual drive ratio with a tire and gear change?

[85K10SB]

Hey all, I'm a new member and this may be a newbie question but here goes.
I have an 85 K10 with a 700R4 + NP208 that WAS originally equipped with the small 28" tires and 3.08 gears. When I acquired the truck the previous owner had replaced the stock tires with 33's. The gearing was so terrible that I couldn't maintain speed on a flat road on OD, and naturally the tranny was running a little on the warm side because it was turning so slow(1100rpm@60). So, I replaced the 3.08's with 4.11's to try and bring the RPM's back to where they were supposed to be. I am now turning 2100 at 60mph, which feels about right. Now my only complaint is the speedo being off. Does any one know what my actual final drive might be. I'm think it's around a 3.73, but that's just a guess. Jus looking for a starting point to get one of those speedo cable ratio reducers to correct the speedo. Sorry for the long winded post, just trying to give some background in case it's needed. Thanks in advance for any responses.

JB