1989 Jeep Laredo back fire and accelerating

The first thing that you should check before wasting anymore money on parts that you may not need is the timing chain. If your timing chain has slipped because of being worn, this could happen easily and is more common than you may think. Have your timing checked. Even though you may have your timing monitored by the computer, if the timing chain slips, then it will cause the problems that you describe. If you had a bent valve, this would be the case too but it would probably backfire or run rough at idle too.

it has new engine one and half year old i dont think it can be the timeing but i will try that it all so hade troubel with the crankshaft position sensor and gave the same prob with old owner i put new one and it still back fire

Check your timing anyways just to be sure. Sometimes even new engines have problems too. IF it is not the timing chain, check for pinched or damaged wires running to your sensors because during engine swaps, one of the wires may have accidently been damaged. God speed. Let us know what you find or if you need more help.