It could be the distributor. Mine did the same, but eventually threw a code for misfire. Get someone to hook up a scan tool while driving it and monitor the timing when it is acting up.

 

When I replaced the cap/rotor I examined the distributor...no side to side play in the shaft (just the required up/down movement) or grooves cut into any of the tower contacts of the old cap. Since there were no codes present I haven't had the system monitored while driving, but I will. I had some free time yesterday so I checked all the vacuum hoses and cleaned the electrical contacts/plugs on the coil and sensors but that didn't help.

 

Saturday I had the mechanic at the local garage hook his scan tool up and we drove around both stop & go and freeway. He said everything looks good and still no codes popping up. He felt the 'hesitation' a couple of times and it has him scratching his head also. He doesn't think it is engine or transmission related and his 'best guess' is that it might be a wheel bearing going bad. Is it possible for a bearing to be going out but not produce any noise or vibration? I had a bearing go bad several years ago on a different vehicle but it made a howling noise.

 

I'm having the same problem...99 LT, 4x4. I haven't done any work yet, but I haven't seen in your postings about a fuel filter change? Since I'm having the same issue, I'd like a possible solution. I'm hoping it not the torque converter or transmission bands. If this blazer even has trany bands! Please re-post with solution if you've found one.

 

Make sure he monitors the timing while driving. It won't necessarily throw a code, but the timing may not be advancing. You won't know if the distributor is bad by looking at it. It has a module in it that advances/retards the timing as needed. It could also be a fuel problem.

 

Bingo!

Sorry...should have followed up on this thread. I must have forgot to mention the fuel filter...it was also replaced. All connections at the PCM and sensors (cam/crank/maf/egr/etc) were also cleaned. After monitoring performance under load it was discovered that the timing was erratic above 1500 rpm. The cam and crank sensors checked okay, and there was no excessive side to side play in the distributor shaft. Knowing it was a timing problem the distributor was removed for further inspection. After inspecting the distributor it was concluded that it was a worn bushing. Even though there was no side to side play when the distributor was in the engine, there was quite a bit of side to side play at the gear of the distributor. A new distributor resolved the problem. I'm assuming that the play in the lower portion of the shaft was allowing it to walk around which caused the erratic timing condition.

 

Awesome! Thanks for the follow up. That's what makes this forum really work.