Osburn 2400 insert Install from hell Please help!

Seeking our next move; We purchase this stove a few week ago the install was a challenge. Firebox was to small took it apart and rebuilt it still very tight concerned about lack of air flow near the rear inlet holes.
The usual damper needed to be opened w/ a grinder and the smoke shelf needed to remove bricks to the lintal. We also had an offset to get the connection to the 6" S.S. flex pipe. Ordered 30' to put down the chimney which had a good draft we raised it about 6' the flue liner for the old fireplace insert is about 18" taller than the flue for the gas fired furnace. We didn't have any back drafting issues after raising the height and it is in very good condition. The 6" pipe did not slid down the chimney we went to plan B and cut it at 6' installed into the flue liner; after all that fired up the stove for the first burn seemed ok. We also could not make the connection to the stove through the 12' x12' access clean out door had to take the whole back of the chimney apart enough to fit inside to do the work.
After a few fires the stove displaces smoke into the room during the refilling process and when the burning Temp. drops. The back of the chimney is still open and understand that is cooling the pipe that connects the offset into the flue liner.
Now is my latest ISSUE loaded the stove closed the damper down and left for a few hour to find the house full of SMOKE open the damper all the way got the fire going had the windows and doors open. When opening the door to add fuel smoke is pouring out into the room.
Took the baffles down the insulation weight was not at the top center of the insulation blanket or lined up under the flue outlet. Was going to take the stove pipe out of the offset to inspect for a blockage however it was fighting my harder than it went in. We did clean the chimney before starting this process. 25 years as a licensed G.C. this project has fought me to the bitter end. Never smoked the house out before. Also shut the fan down and opened window when filling the Stove.
Please review this and advise me to correct this issue. THANK YOU

Thank you for you input, yes it was warm, the wood also might not have been as dry as popcorn. as I have been reading and learning no more newspaper to start the fires. I used to use a torch and some oil soaked rags from the garage. Another thing I used to do was take the wood chips, dust bark and put into a box mix in some cooking oil for the waste oil burner and that would get the fire hot quick.
New to this site and appreciate all the advice hope to be burning for another 40 years.

Gentlemen;
Thank you very much for your input;
So that it will be clearer most of my issue is that fact that the 6" Stainless liner We still have installed only to the first liner because it would not slide down the 25' needs to be forced down and the problem is when I shifted to plan B cut the liner and ran it only inside to the first flue liner there is a break in the vacuum effect of the chimney. (Please explain what exactly is the meaning of the term Positive Flue Connector into a Masonry flue)? I also thought with the warmer weather and the back of the outside of the chimney open that also is not helping with my draft and was part of my issue also will the wood not being popcorn dry. It did work fine for the first few days with the damper mostly open all the except when the stove was getting too hot.
Can we slide a 5.5" stainless liner down the chimney and connect that to the 6" Stainless liner already installed? I think the 6" was getting hung up on the flue liners not being exactly flush and some masonry mortar sticking into the opening. I sure there is a trick of the trade to force it down however I am hung up on this learning curve.
Again Thank you all for you time, help and advice!