Misfire when accelerating

SOURCE: My 1999 alero sounds the engine is misfiring

2.4 liter OHC coil housings have this as a common failure. Thery arc over internally to another cylinder and cause the misfire.

SOURCE: bucks or jerking feeling cruising at highway sppeds

It sounds to me like the drive train is getting loose. By loose i mean that the universal joints, and linkage to the rear differential is worn.
The engine speed is trying to adjust to keep the speed sensor from the transmition to the cruise, and the speedometer constant. when the engine begins to slow down, or speed up the loose drive tran will be amplified by the loose linkage. It is easier to notice this problem with a standard transmition.
If it has a stick shift and you are in a low gear try speeding up and then letting off the accelerator and it will ****. If it has an automatic it will not be as evedent but you can try putting it in the lowest gear and do the same. It could have a clank sound when you hit the gas, or when you let off the gas, but not always the case. If the universal joints are going bad it may have a vibration when you get up to 40 MPH or so. This will shake things apart if you wait too long.
Also if the universal joints are wearing out it could have slop in it when you have it parked and give it a strong wiggle from the drive shaft just in front of, or just behind the universal joint.

SOURCE: car chugs and jerks like crazy while cruising

Determine whether the jerking is engine or transmission related. One way to determine if it is the transmission lock up converter is acting erratically is to down shift out of OD. And see if jerking persist. If it goes away suspect transmission to have problems with torque converter or TCC solenoid . If it doesn't go away determine whether or not the engine sounds to be misfiring. If so vehicle may require a tune up. Many vehicles can be diagnosed for free at your local Auto Zone.

SOURCE: when driving on the highway

Bad COP Ignition Coils (cylinder misfires) even if you have
no wrench on the dash (check light)

Check with scanner in MODE $06 on a road test
or use an oscilloscope on coils

Egr Valve -- not any good also ,if it has been there since 2004

SOURCE: Car jerks while driving on the highway. Seems like

Old adage is.....misses on a pull.....it's ignition. How old are spartk plugs and wiring?
The car is also old enough to have some vacuum lines getting broken or brittle.So check for vacuum leaks. don-ohio