Chris,
No problem, happy to help out. Since you are new to the OM603 engine, I'll mention one last thing. Do not EVER let it overheat. The original aluminum head design was flawed and will crack fairly easily (compared to the old iron head, which was almost indestructible). MB redesigned the head 3 times and the gasket 5 times. Normal operating temps are 80-100C under almost all conditions. Under blistering heat with the A/C on climbing a mountain, you may see 105-110C but that's it. Anything more, or if you see those temps when it's cool outside, and your cooling system needs attention. The fan clutch tends to die after ~10 years and the radiators plug internally if you don't use MB antifreeze and change it every 2-3 years. If you have the evil "green" stuff in there, get rid of it ASAP. The MB antifreeze is a special formula for iron & aluminum components, unlike ANY other a-f on the market. It's only ~$10/gallon so $10 per 3 years isn't bad insurance. If the fan has plastic blades, the clutch is probably recent. If not, watch the temp gauge!
Now, about the cold start. If it's just the first 5-20 seconds after startup and then it's OK, try letting the glow plugs stay on longer before cranking... let them heat up 5-15 seconds more AFTER the dash light goes out. Then start up. If that has NO effect, either you have carbon buildup around some of the glow plugs (reducing their efficitve heating ability, regardless of resistance measurements) OR you may have a fuel injector problem. Glow plugs should measure 0.6 ohms each. Driving the car HARD is good for the engine and keeps carbon cleared out, so "drive it like you stole it" as much as possible - trips to the redline are GOOD for it! Really! I find it odd that only 3 injectors were replaced. Worst case, you pull all 6 and have them pop tested at a diesel shop & checked for leaking, good pattern, etc. The compression should be good, these engines rarely have worn bottom ends if maintained well (regular oil changes every 5k with dino, 10k with synthetic, more often if city driven).
Finally, yep, this is a VERY good Mercedes tech board. The other resource I highly recommend is the MBZ.org diesel email list. The traffic is fairly high so sign up for the digest version. There are several folks who have small fleets of OM60x-engined MB's and the collective knowledge is fantastic. Also play with the "search" function on this forum, there is a TON of information in the archives, you just need to find it!
Good luck,