There are a lot of things that can cause your hesitation issue.
You run fine when cold because you are in open loop and the controller is running on a fixed program.
Once warm the vehicle goes into closed loop operation and the controller now pays attention to the O2 sensor.
1)Are any fault codes stored?
2)Cam/Ignition Timing
As already stated above 1 tooth off on the cam sprocket will make a big difference.
This seems to be a major area of confusion and time lost during install or diagnosing as to weather the Cam is truly aligned properly. There have been numerous threads over time that the OP said the Cam timing was verified to be correct (checked it 3-4 times) and after a 4 page thread and...
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3)Ignition System
Weak Coil, Excessive Secondary Resistance (Cap/Rotor/Wires), Worn/Fouled Spark Plugs
KV Requirements increase on acceleration, if the system cannot keep up due to any of the above mentioned items then a hesitation will occur.
I suggest using an Adjustable Spark Tester to check system capability and physically checking the spark plugs.
Open the spark tester to 30 KV (system is capable of 40 KV) and check at each cylinder.
Shop for OEMTOOLS Adjustable Ignition Spark Tester with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.
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4)Map Sensor Circuit
The Map Sensor is the Dominant Fuel Control Sensor.
If the Map Sensor Calibration is incorrect (Either Baro or Pressure) or there is a restriction/leak in the Map Sensor Vacuum Reference Line you may/will have the issue you are currently having.
I am posting this so I do not have to keep typing this over and over and will make it easier for members to find help on their own. Fault Code 13/14... No Change In Map Voltage From Key On To Engine Start Map Voltage Does Not Equal Throttle Position. Map Voltage Low Map Voltage High Map...
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5)Fuel Pressure
Fuel Pressure on a 86 - 91(1/2) TBI is 13-15 PSI and remains steady at all times.
6)Oxygen Sensor Operation
It is rare for an O2 sensor to cause a driveabilty issue (since it is only a fuel trimmer) other than lower MPG and cause high CO emissions, however...
If the O2 sensor is latched above/below .450 volts or extremely slow to respond then yes, it may cause your hesitation issue.
The job of the O2 is to inform the engine controller of oxygen content in the exhaust stream so the controller can attempt to keep the A/F ratio at 14.7/1 (Stoichiometric) in closed loop operation (idle, no load cruise)
The controller makes small corrections in the fuel mixture to try to maintain 14.7/1 and that is why the voltage will constantly cross above/below .450 volts.
Just remember, the amount of oxygen in the exhaust stream is determined by how well the engine is running so O2 voltage will be affected by any of the above items mentioned.
Once you know all of the above items are OK you can check O2 operation.
Tap into the O2 sensor signal line with a digital voltmeter.
On a warm engine voltage should constantly cross above/below .450 volts as the controller makes small fuel corrections.
