1969 Chevy Camaro Clutch trouble

Hi. I have a 69 camaro with a 396 engine and a muncie m20 4-speed transmission. I have a center force dual friction 11 inch clutch, gm clutch fork; and a lakewood blowproof bellhousing. I am having trouble getting the car to go into first gear easily when hot. When the car is cold; I can shift through the gears very easily. Once started and warmed up, I have trouble if I go from neutral, third or fourth to first gear. An example would be going 45 mph in fourth and coming to a changing light. I cannot go from fourth to neutral; put on my brakes for the red light; and then push in the clutch to go to first once I stop. Sometines the only way for me to get it to go into first is to go to reverse, then neutral, then it will go into first. But this gets old. It does fine if I go from fouth to third to second to first. I just can't go to neutral from third of fourth and then to first once I get stopped. I have a brand new muncie m20 four speed built because I thought it was a transmission problem. But old and new trans. Are the same. I have checked my clutch ( which is not that old) and it looks new. The pressure plate looks fine. Is my problem possibly in clutch or linkage adjustment. Thanks for your help!

Rob