Conversions & Hybrids - Unusual temp problem

I put a 6.0 LQ9 in my 68 vette, In order to keep the original gauges, I tapped the block plug on the drivers side for the sender. It's 3/8 NPT and the probe sticks in too far to tap the passenger head. I'm also running the big truck mechanical fan along with a computer controlled electric.
I'm running a much larger than stock aftermarket radiator and LS2 thermostat.
When accelerating (even from a stop light) or running over 2000 rpm the temp quickly goes from about 190 to 220. At hiway speeds (about 1900 rpm), it will stay at about 210 or will drop back to 190 if cruising at lower rpm (1600 rpm). The elevated temp seems to be rpm related.
Right now it's only 60 degrees outside, but I'm worried about summer and running the AC.
My IR temp sensor doesn't see anything over 195 anywhere on the engine, water pump, hoses, etc. The cold side of the radiator is under 100 and the radiator/fan is well shrouded, the fan clutch is new. The computer never turns on the electric fan (Not sure of the 02 LQ9 computer setpoints though).
Is the temp sensor mounted low in the block giving false readings for some reason?
The only other thought is the amount of oil in the pan. I went to a 02 vette winged pan/pickup/dipstick/tube and discovered it takes 10 quarts to show correctly on the dipstick with the LQ9 block. So now I'm running the original 02 vette 6.5 quarts.

you are able to read what the pcm sees, correct? thats what is most important. i ran a fitting in my passenger side head and the guage is usually about 20-25 degrees off from what the pcm sees!

"I'm also running the big truck mechanical fan along with a computer controlled electric."
Why do you feel the need for the 2 fans?
Where is the elec mounted?
Is the rad below the top of the engine? If so, you may have airlock.
Do you have a way to purge, in addition to the stock steam lines?
Is your engine equipped w/ steam lines at both ends of the heads?
Where do you have the steam lines connected?
Heater lines hooked up?
As Jomomma said: Are the temps reported from the 68 dash, or from the pcm?
Have you had the engine tuned?
Do you have a scan/datalogging program?

"I'm also running the big truck mechanical fan along with a computer controlled electric."
Why do you feel the need for the 2 fans?
Where is the elec mounted?
Is the rad below the top of the engine? If so, you may have airlock.
Do you have a way to purge, in addition to the stock steam lines?
Is your engine equipped w/ steam lines at both ends of the heads?
Where do you have the steam lines connected?
Heater lines hooked up?
As Jomomma said: Are the temps reported from the 68 dash, or from the pcm?
Have you had the engine tuned?
Do you have a scan/datalogging program?

Mechanical + electric because that's what as used in the 02 escalade, old vettes are notorious for overheating (I used the electric on my SBC + mechanical, they worked great), and I wanted additional cooling with the AC. Electric comes on with AC refridgerant pressure (trinary switch) or computer high temp signal (not sure what temp the 02 escalade used).

The electric is a puller inside the radiator shroud.

Radiator is below engine but I've got a inline fill/pressure cap at the highest point. I can purge all air out (excellent question on vettes).

02 Escalade LQ9 had front steam vent only. I've got that plumbed to the water pump.

Heater lines are hooked up. Heat works, hetaer control valve is open with heat, closed with AC on.

Temp is from the dash gauge with sender at drivers side screw in block plug. I do not have a scanner to read the computer or it's sensor temp. I had an aftermarket tune to eliminate VATS, etc, the harness did include the stock electric fan circuit.

I went and bought a gauge and hooked it to the passenger head boss. Even though the new vette gauge and sender are reading 190-220, the heads were at 160-180 degrees by the aftermarket gauge AND by IR temp sensor. Btw, heads at 180 but coolant exiting water pump was at 195, so it looks like everything is ok. I may be picking up some heat from the exhaust manifold that's near the lower block plug where I mounted the sensor.
Thanks for the help guys!
Gary