Engine dropout at 1800 rpm and at approx.2500 rpm

Hello , I know I'm new to you, but I've been driving a V8 3.6 for a year and am very satisfied, since Betieb with LPG also almost cost-effective.
Recently, the car is bucking at 1800 rpm and at approx.2500 rpm, according to the error memory, the speed sensor and the cylinder detection. OT encoder and speed sensor I have reinstalled, but no change.
If you are fully accelerated, you can't notice anything, only in normal driving mode it has dropouts, and in idle mode you can see the tachometer pointer sucking off.
All underpressure hoses, ignition cables distribution caps and runners were replaced by me during the LPG conversion.
Who can help me??