as the title says, my friend has a 99 blazer that hesitates when cold. He had the trans fluid recently repalced but not the filter. Im thinking it might be the spark plugs but not too sure. It has about 120k miles on the engine.

This hesitation occurs right before the 1-2 shift. feels like if it was the fuel pump. like it wants to die because of lack of gas! No CEL on. awd doesn't work. wat u think it could be?

If it needs a basic tune up do it.
Good ac plugs and fuel filter air filter.
I would check that fuel pressure.
And post back pressure readings.
Also get it on a good scanner and check out for codes and sensor readings.

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

thanks mt-2500 i will try that and post back as soon as i do it!

ok. we replaced the spark plugs with ac delco ones! the problem is still there!

We get a check engine light on now! code p0300.

cables are pretty new.
cap and rotor seem fine. no carbon traces. recently replaced.
we replaced the notorious lower intake manifold gasket about 5 months ago. i think the problem was already there but was not too bad.

This hesitation only happens when the truck is cold and right before the 1-2 shift! once the truck warms up no more hesitation. this accompanied with a check engine light but comes and goes! wat could it b?

Make sure fuel pressure is up to par.
If so see if you can find the engine miss.
Can you feel a miss or short out the missing cylinder?
Good hot blue fire to all spark plugs?
Camshaft retard setting?