It's worth checking the TPS especially since you said it's going in and out of overdrive.
I finally replaced the pigtail off the harness because the female pins in the connector were messed up. Sometimes it would run good and it would usually idle high around between 1500 and 2000rpm after touching the throttle for the first time. It would usually shift in/out of overdrive if I was close to 45mph. Then again sometimes turning it off and restarting once it was up to temp would make the problems all go away.
Figuring out it was the TPS took me over a year(stupid '95 that can't connect to a reader). Just because it tests good with a meter does not mean there is not a problem. You could also check the ground(s) on the engine. Sometimes a bad/dirty ground can cause some strange issues.
It sounds like you have most of your bases covered. Keep at it though.

 

Nope, shouldnt be a difference

 

Thanks guys appreciate all the help. I will change out the TPS and go from there I will update as soon as I get it in! Thanks again
Shane

 

So tom I am going to install the TPS to try and fix this in and out of overdrive issue. I also wanted to say that if the blazer has a full tank of gas my hard start issue vanishes and I have yet to notice the bogging down and loss of power after hard acceleration thank the car gods lol so im not getting fuel on initial start up and im leanimg out with hard acceleration.now my question is why? Why would it start hard first crank of the day but then no problems starting later? How is it that my fuel pressure test was normal so was the leakdown? Why would it change with a full tank? I know I probably need a fuel pump now but I was wondering if anyone could answer those questions so I have a better understanding of what is actually happening. Thanks guys this forum is freaking great and has helped me in returning my blazer back to the beast I love"

 

I think it could be the ECT sensor causing the 'hard start when cold'. Then once the engine is warmed up, the hard start goes away.The ECT is sorta the new equivalent of the old choke.

 

Jim,When hooked up to a scanner after 12 hr sit over night both AIT ,ECT both read the same about 1-2 degree difference from ambient temp. Both sensors seem to be working but it's something I could change out being they are pretty cheap thank you for your reply. Some more items replaced as of today are Alternator, belt tensioner, idler pulley, belt, ignition switch. Will update more on hard start when I change out fuel filter and run another pressure test. Thanks again
Shane

 

I was re reading your posts to see what you have done to this Blazer. Why? Because that is how I introduce new problems in with the original problems. I was seeing you had replaced the cat because the old one was clogged. I was trying to think what would cause a cat to clog and cause your existing problems. O2 sensors are one item , but they don't cause hard starting. They don't enter in the picture until the engine is warmed up. Anyway, recheck your work and make sure the connections, splices, and so on are correct. Good luck and let us know how it turns out.

 

Jim , all of my symptoms have been the same before I started fixing things. Prior to the items mentioned above I was throwing P0300 P0305 started at the usual suspects and it got better with no codes so I figured wth I keep going and replace what's not working properly or so I know I got a good part. The cat had been rattling a lot then all of a sudden stoped. The garage pulled it off said pieces were stuck in cat and in resonator so I had them replace them. The alternator was squeaking bad and voltage was everywhere my dash lights wouldn't come on sometimes so I replaced ignition knowing that 97 had a problem with them.After everything has been done blazer runs better then before. Just hard to start sometimes mainly when tank is low. After hard acceleration I lose power and it Boggs down then smooths out still trying to sort these two out. Thanks for your reply and I will continue to update what I've done .
Shane

 

Still having hard star when cold. It's been 45+ for a couple days had no problem! It was 19 and it cranked slow and took like 6 cranks to get her running. Battery tested good this is driving me nuts. Battery or starter or none and just have to get used to the hard start ?

 

I was having this issue all winter also, and decided to just deal with it. Then I changed my starter and all is good now. Think it was just old and tired. original 210,000 miles