We always run Pennzoil Synchromesh in the T56, T56 Magnum, and TR6060 transmissions. The T56 takes 3.9 quarts, so go ahead and get 4!
Pennzoil Synchromesh Fluid is designed to offer optimal protection for moderately loaded gears in manual transmissions. Containing a high detergent additive system, it helps cope with water, dust, dirt, and any other small deposits you might encounter on or off-road1. Pennzoil Synchromesh Fluid also offers synchronizer compatibility for performance in manual transmissions, specifically to fulfill the needs of Chrysler, GM, Honda and other transmission requirements.
Pennzoil Synchromesh Fluid meets General Motors specification 9985648 for use where GM part numbers 12345349 or 12345577 are called out for use. Chrysler manual transmission fluid specification MS-9224 is also met. This high quality manual transmission fluid is formulated for good low temperature flow to maintain shift characteristics even after a cold night2. Corrosion protection is added to help protect your transmission.