Hi Bloomfield
I had my Ricoh tech in yesterday, Friday, and I mentioned this post to him as he has worked on the c71xx from new and he was quite surprised to here you were having issues on textured stock as he has had no complaints from his clients.
How textured is the stock. He did say that on heavy textured paper you may need to adjust the AC transfer bias more to the negative side, by which I mean you need to go from -150 to -250 for example. Also on my c9110 I have a setting called Paper Transfer High Pressure Mode which is for textured or thick paper, do you have this setting in you advanced paper settings, might be worth a try if you do.
Another thought, do you have settings for image transfer. This adjusts the amount of toner that goes down onto the Image Transfer Belt that pushes in to the paper. If you increase the negative number as above it should place more toner on to the belt and hopefully on to the paper. You may also have a setting for toner adhesion which goes from -5 to +5 if you go towards the positive will also help lay more toner on the Image Transfer Belt. I have had to use these settings in the past to bump up the black (K) for certain jobs as out of the box solid blacks on the c91xx aren't the best. For one job in particular I raised it up to +4, I also raised the image transfer bias from -60 to -80. Along with increasing the paper transfer bias to make sure the extra toner goes on to the paper.
I also forgot there are two paper transfer currents, The paper transfer Current and the Paper Transfer Current AC both of these need to be altered, more or less the same, and its best to increase the 2nd side slightly more than the 1st.
Also I have used the term Bias instead of Current. When dealing with techs we always use bias but the menus use current. Sorry if there is any confusion.
Hope some of this helps but if your tech can't sort it you need to get it escalated and get a Ricoh expert in.