3.2 gr. of HP38 / W231 is the minimum starting load for 148 swaged (soft lead)wadcutters in the Hornady manual for a 38 special. As you found with 3.4 gr., that is questionable in hard cast lead and will definitietly be a problem with plated. Xtreme brand uses a thick plating and harder lead cores thus they are more like jacketed bullets then lead.
WARNING, the following is based on my personal experience... USE at your own risk. Neither I nor TFL assumes any responsibility for the results.
With a 38 Special (I know you stated 357) you should do the hard cast at about 4.0 grains starting and 4.5 - 4.6 will be a 38 +P load. The fact that you went shorter than book and still squibed should be an indication that your pressure is substandard.
With the 158 gr. SWC. you can make a nice light / mid range 357 load with 5.4 grains of HP 38 / W231. This will certainly be more than a 38 +P. You can push this farther about 1 grain more with swaged lead and 1.5 gr. with a jacketed bullet and stay within published data. With the Xtreme plated bullet, I would be looking at 6.5 grains to be around max. for a novice.