About all that is left is cranking speed.
Make sure you have the correct size battery (probably group 24), but it is larger than the group 26 whatever it is. And that the battery connections on the inside where they meet the posts are shiny clean.
Perform a load test on the battery through the the cable ends. You can use the starter lug.
Also check starter connections on the red cable and the ground on the block.
Perform a load test clamping to the starter lug and block ground's bolt head.
Make sure the fuel enrichment solenoid is energizing by touching it with a screwdriver to verify it becomes magnetized. Open that connector and tighten the connections in there, they are often loose. A long crank time, or second crank time could drain the battery and cause a slow crank speed on attempt 2 but not attempt 1.
Check the time of the error and compare it with the set time of the exercise to determine whether it occurred instaneously, or several seconds in, or on a subsequent attempt.
example exercise set for 1200 Saturday.
Fault at 12:00:10 = Instantaneous
Fault at 12:00:16 = Detected at first then lost
Fault at 12:00:28 = Loss during second attempt
Turn gas off and simulate multiple crank attempts if you suspect that it may crank fast at first, fail to start for some other reason, then lose its crank speed on later attempts.
State your problem, not your diagnosis.