Cool at idle, gauge reads hot when driving?

[68 Greenie]

Ever since I installed my 383 with this 292 cam with .501 lift my factory gauge shows it running hot after just driving down the block. I have a rad cap and it only shows about 150 but my gauge inside just keeps climbing but when I stop to idle it goes down. I have an aluminum radiator with duel cooling fans. I had a temp. ascending unit from and 86 installed in a port in the intake. My motor by the way is a 86 block. I today installed the correct temp. ascending unit for a 68 but I had to put it in the top of the water pump and it still does the same thing. Could it be a bad gauge? I have also been told that my 600 edelbrock performer is not enough carb. and may be running to lean so that might be why my gauge goes up when driving and down at idle. I have never heard this but im not ase certified mechanic either. I need help getting very frustrated and don't want to destroy my new motor. I really appreciate your guys opinions, it helps but this one has thrown me for a loop. Thanks.