I have a tech-4 true blue 90 furnace. The problem I am having is that the blower shuts down during the heat cycle. The burners keep running after the blower shuts down until the high limit switch shuts them down. Immediately after the burners shut down the blower comes back on and the burners will fire up again, this continues until the thermastat temp. is reached. I can turn the fan to manual and the furnace will run right up to temp. and then shut down (fan still running of course). Fan makes no noise and will run all day on manual.

Assuming you have a multi-speed blower motor, my first conclusion would be that what ever speed you are using for heat is failing. Motor starts up and runs but pulls high amps and then eventually goes off on internal overload protection. When the motor stops CAREFULLY reach your hand in and feel the motor. Not the squirrel cage but the actual motor housing. If it is hot then chances are you will need to replace the blower.

Replace the blower lol. There is a joke in there about wives/girlfriends/significant others but I'll keep it clean.